Advice??

I used to enjoy sex and now it doesn't excite me to think about it. My boyfriend got frustrated with me tonight about it because he was ready to go and it just didn't feel right to me so I made him stop. It felt so tight it was uncomfortable to me while he said it felt extremely loose so he thought I had done other things which I haven't. I feel like something is wrong with me,but I don't even know where to begin... any advice is greatly appreciated.