what's going on???

so whenever me and my boyfriend have sex and we're doing it doggystyle, he'll sometimes spread my butt cheeks and it hurts! It feels like the skin tears or there's like a cut in between my crack! I don't know what this is or why it happens but it kind of concerns me??? I saw online this might be a yeast infection... Can anyone tell me if they've experienced this and know how to fix this!!