No Stupid Questions

Being sore doesn't mean that muscle is being built, that's a misconception, it's actually muscle being damaged.

Soreness is micro-lesions in your muscles, and what builds them stronger is actually the rest following a workout. Because that's when the body goes around to repair these lesions and builds stronger bonds within the muscle.

What builds muscle is resistance, nutrition and rest, the latter two being the most important.

You can't build muscle if you don't feed them right and give them time to recover.

So, killing yourself at the gym 3/4 days in a row, focusing on the same muscle group is actually really counterproductive.
Rotate your training focus with a split like push/pull/legs/core, or upper body/lower body/cardio, or whatever, as long as you enjoy it.

Give yourself time, eat right (as right as you can, don't fall into the rice/chicken at every meal madness, balance is key), sleep a lot, take some rest days and deload weeks once in a while, and drink plenty of water.

And most importantly, be kind with yourself, it's a marathon, not a sprint, you might struggle going to the gym some days, but showing up and doing less is better than not doing it at all.

AFAIK you should alternate your training. Muscles need rest. The actual buildup of muscles happens when they rest, not during training. So a day break would be advisable if you are not a body builder or otherwise professionally.

Give the sore muscles a break until they're not really sore anymore, it will save you future joint pain. A specific amount of time isn't what is best, it's the amount of time it takes to recover, however long that takes.

Don't push past form failure either, once you can't do the movement properly its time to go down to smaller weight or move on.

I've trained my arms for 3 days in a row, nothing fancy: upright rows, bent-over rows and triceps kickbacks, 10 repetitions each, 2 rounds. After that I'm so sore I cannot do more, so I turn to cardio and do planks (front and side) and some yoga.

Really recommend finding a workout split. I do push, pull, legs x2 and an hour on the stationary bike on Sundays. Monday is push, so my chest, tris, and shoulders are all hit. Then they’re rested the next two days when I get back to push. You could do also do a bro split or just find something that works best for you. The important part is that you’re giving your muscles time to rest between sessions.

On that note, the most effective way to gain muscle is to be in a calorie surplus, train to failure, and progressive overload (and steroids). So make sure you’re gaining weight (slowly, don’t just start bingeing cake). Push your sets to the point where you can no longer keep form. Try to lift more than you did last time (either more reps or more weight).

Don’t skip legs. I don’t mean cardio, do some actual resistance work on your legs or prepare to find yourself top heavy. “Skipping leg day” is a meme for a reason.

As other have mentioned, you need to rest and make sure you eat proper nutrition. Protein helps repair/grow muscle along with sleeping. Your muscle needs rest days.

Look up some gymnastics arm workouts, if you want to switch up some moves. Doing bicep curls while keeping your arm straight is a good arm workout. You don't need much weight for it either so it's easier on joints.

Go swimming... Much better overall and pair wonders with running!

... Then pickup cycling and start triathlon...

Look to the way bodybuilders train; do only 1-2 days each week, max, per general body part. I would suggest something like doing back and biceps on one day, chest and triceps on another. (Back exercises usually involve pulling, and that uses the biceps, so you would start with large compound movements--like bent over barbell rows--and progress to more isolating movements, like preacher curls.)

The general concept of 'toning' is a serious misnomer; you need to either add muscle mass or cut fat; both of those will make the muscles more prominent. You can't realistically do both at the same time without significant chemical enhancement, and I'd recommend against that.

As far as cardio goes, I think that 5-6 days/week of cardio is fine, depending on your intensity. LISS cardio can def. be done daily, but you should have at least a day between any HIIT sessions to allow your body time to recover. If your running is all at a conversational pace (you can talk fairly easily; I've never been able to achieve that, even when I was bicycling 30 miles/day), then daily is great. If your heart rate is >75% of your maximum, then every other day. You might want to add in other forms of cardio as well, like rowing, which is going to also involve upper body.

Soemthign else to consider is getting a personal trainer. If you do that, look for one that has a certificagtion from the American College of Sports Medicine or National Strength and Conditioning Association, in addition to at least a BS in a degree like exercise science of kinesiology. Most PT certifications are absolute bullshit, and in the US, none of them other than ACSM or NSCA are worth a damn. If you choose to hire a personal trainer, be very, very specific in your goals, and make sure you get programming for all the days you aren't working with them. Most PTs will try to sell you as many sessions as possible, which is great for them, and not so great for your wallet, so set your expectations accordingly.

Ensure you have lots of bioavailable protein from a clean source

Exercise a muscle group to the point where you feel the pump after, rest that group until you don't feel the soreness anymore.

Repeat.

Avoid sugars, keep your insulin levels low (I know body builders when they do bulking ignore this), and you will build lots of lovely muscle.

If those are the only arm workouts you're doing, you're really just working your triceps. Need some pulling motions for the bi's.