I'm still nervous that i'm pregnant!

Hi my name is liz. My boyfriend and I had sex back in february but i think that the condom might have broken or something. My period was 6 days late, which is not unusual for me. However, I'm worried that it wasn't actually my period and just implantation bleeding or something else. A few weeks ago i was supposed to get my period again but it was 12 days late (which is pretty late for me). I was extremely nervous about being pregnant before my period came that i took a pregnancy test (negative). During that time, i also went to the doctors office for stomach pains and they ran some blood work (everything was negative). Now I'm still nervous that i'm pregnant, and i've been feeling nauseous lately. Please, anybody, tell me if i'm just making this up in my head or if there's actually a chance of me being pregnant.