Bigger nipples?

okay first some background info: I'm 18, I have no children and im on birth control and use condoms so the chance of being being preganant is very very little.
I have noticed a change in the size of my nipples, especially when they're hard (ex. when i'm in the shower). My boyfriend often plays with them and sucks on them whenever we have sex which is probably around 5 times a week. Is it normal for my nipples to get bigger since they're being stimulated so much recently?