Zero sex drive - why?!

Background info - I'm 19, in a relationship of 2 years, been sexually active for 5 years, also been on the pill (microgynon) for 5 years. The last few months for some reason I just have no sex drive at all. My poor partner only gets sex maybe twice a month if he's lucky and even then it's clear I'm uncomfortable which ruins the mood. I have no interest in pleasuring myself whatsoever and just don't feel the need. I love my boyfriend and sometimes I do start to feel a little turned on but it's not enough to have pain-free sex. It hurts inside as if he's going too deep and it hurts outside as if it's tearing because my vagina just isn't fully relaxed. We used to have sex twice a day, we've had threesomes, we've had sex in a lot of weird places, I've dressed up. But lately I just can't be bothered. It really does just feel like a task. I know it's upsetting him and I know it's an important part of a relationship but I just have no desire to do it recently. Someone PLEASE help because I really don't know where this has come from or why it's persisting. Ive been feeling this way for a few months now.