Sudden low sex drive?

I’ve been dating my boyfriend for quite a while now. We are pretty serious, and spend quite a bit of time together. When we first got together, we were having sex 3-4 times a day. I mean, it was exhausting. But, i had the stamina and sex drive for it. Within the last month or two i’ve noticed a significant decrease in my personal sex drive. My boyfriend has expressed that he is sexually frustrated, due to us not having much sex, and i’m not sure what to do. Yes, i am attracted to him and i love him, so why am I never in the mood? Is it birth control? Medications?