could I be prego??

I want to start off by explain when I last got my period it was on April 13 and ended April 18 then rite after starting on the 20th to the 23rd I had unprotected sex and I'm not on any birthcontrol at this time so I waited until April 26 and hade a pregnancy test done at the clinic my doctor told me it was negative because its way to early to find out if I'm preganat or not so she made a follow up app. And told me to come back on May 17 she said a good time to find out if iam pregnant or not is if I miss my period okaii so I've been waiting and on May 13 which was a couple of days ago I was supose to get my period and I didn't so the next day I bought a pregnancy test and tested negative do you think its still to early to find out if I'm preganat?? Tomarow I have my follow up appointment...I also don't have any symtoms of nausea or dizzyness I just feel a lot of cramps and my back hurts a lot