No sex at 20

im 20 and have been in a relationship with my b/f 2 over 2 years when we first got together we was havin sex all the time but now we only have sex about once every 3 to 4 months and thats me who cant bring myself to havin it but when i do i really enjoy it and if im not really in the mood and it gets going then im fine but the thought of havin sex i just dont wanna do it. anyone have any answers

On the pill?

Are you on the Pill or any medication that might be affecting your sex drive?