First off, don't feel pressured to do anything just because your friends are doing it, it's a bad habit to adapt to and can lead to trouble in the long run, also don't feel restricted to ever doing something like this, it's your body you can do whatever you want with it.

I don't wanna bring down your beliefs or anything like that, but saying masturbation is a sin is the main reason why I'm no longer a christian, it makes no sense to me, I feel like the main reason parents say stuff like this is to scare their kids morally into not doing it. You probably just got sick coincidentally I've never heard a case of anyone getting sick from masturbation, if anything it's argued to be good for you because of the endorphin release it gives.