Issues having an orgasm

So for about a LONG month I have been having issues achieving orgasms when my boyfriend and I have sex. Before this I had no issues whatsoever, maybe every once in a while when I was stresses out it would take a little longer but all in all our sex life is great. But recently I haven't been able to and it's frustrating the heck out of me. Ill feel like I'm about to, feel it start to build, and then all of a sudden the feeling will just stop. Does anyone have any experience or tips? Thank you!