What can be wrong?

So my period is late three days now. And yes I took a test and it was strong negative! I have a watery clear discharge. My mid back hurts and we hve been pretty careful with sex. (Pull out method) I know but still pretty careful. I’m tired and dizzy/nauseated. My head hurts a bit too but that’s normal for me. I’m very gassy. Have any of you had these symptoms and not been pregnant or at east tell me what I should do?

Update- I should mention we are trying/ not trying to get pregnant.