Trying to pinpoint gestation

My last period was May 11th 2014. My cycles are usually 21-25 days more or less. June 20th came around with no period, so my doctor did a blood test which came back negative. I spotted for two days after that. Now on July 12th I had a BFP at home! I didn't chart or keep track of anything the past two months so I'm really lost. I could be anywhere from 3wks-8wks! I see my doctor tomorrow, but still lol. It's driving me crazy