Because you used more of your time early on, where they saved theirs.
Every turn you get a certain amount of time added, if you take less than that time to do your turn, then you wind up with more item after your turn, instead of less.
So basically, they're all making their turns very quickly, where you're taking a while with yours. Try to figure out what you want to do on your turn ahead of time, while others are playing so that you take less time on your turn