Receiving oral and pain??

Ok for some reason I rarely ever get pleasure from receiving oral. No matter what my bf or past partners have done I always end up feeling a little pain and rarely any pleasure. I’ve told my bf and have him do different things but it all ends the same. I had one experience when he did it and it felt good but since then it hasn’t. It’s not just with him either with other ex’s I had the same problem. Is something wrong with me? What should I have them do different to make it feel good?