Hi Sofia,
I'm 22, and I've had this probably for a good 5 years. It's the worst when I am nervous or anxious, but on a daily basis, my underarms just sweat so much. For whatever reason, my right is the worst. Oddly enough, I have a cousin with the same thing, but it's her left. It's called hyperhydrosis, and some people get botox shots to paralyze their sweat glands. There's a prescription deoderant you can get from a dermatologist called Drysol. It's like an alcohol smelling roll on that honestly hurts sometimes if you use it right after you've shaved. It is the only thing that works aside from botox and surgery though. It doesn't stop the sweating completely, but if you use it consistently, it will make a noticeable difference.
Editted to add that I feel for you. This is such an embarrassing problem. It is annoying as well when you start to worry about what shirts you can wear!
Hope that helps,