painful sex- no sti's??

I've been experiencing really painful sex with my boyfriend. I was tested and I'm clear of all STI's. I took medication for BV but with no success. It's like a deep pain on my inner vaginal walls. When he puts the tip in it feel like it's going to be good but the second it hits a certain depth it's almost unbearable. It also seems to sting/burn when he cums inside me. He's been tested and he's clean too. Any ideas on what it could be?