Help? Pregnancy scare

I've been stressed out a lot due to me thinking I'm pregnant. I was suppose to start my period on May 7 and I haven't started... I took 3 pregnancy test already and they all came out negative. I took first response on the May 11 and negative then took another one on May 13 and still negative & finally took another PT on May 18 and still negative. Is there a change I am pregnant? My boyfriend and I had protected sex, he used a condom on. And it was my first time having sex. Someone help me. I have a doctors appointment on Monday May 23rd to see my blood results but still nervous.