can't get aroused during sex anymore?!

i have been with my boyfriend going on 5 years now. we have always had a great sex life. over the last 6 months or so, i have a very hard time getting aroused during sex and it has become very painful for me.

i am on a birth control pill (lo estrin 30) i have been on it nearly 4 years. i have never had this problem before.

it's not just with my boyfriend that i can't get aroused, i nearly never get aroused anymore even on my own. whats going on with me? could it be the birth control pill?