My boyfriend is alway horny

Every time my bf comes to see me he's always horny and wants to have sex sometime we end up having sex 3 time a day or even more seems like he can't have enough. For example last night he kept telling me he wanted to have sex but I would refuse (I'm on my period but last days very light) but just to make him happy We ended up having sex. I didn't enjoy it at all it was very painful, Sometime I feel like he's just using me, any advice?