My last period was August 24th and lasted until September 2nd. I had s…

My last period was August 24th and lasted until September 2nd. I had sex on September 1st and 29th. I saw the doctor on November 27th and the urine test came back negative, then positive, then back to negative within a minute or two. It's normal for me to go a month without my period. I told the doctor that and she said that I could have my period one month then sometime in the next month I ovulate... I did a test yesterday (November 28th) and it came back positive. I've taken a blood test but also the others I've done have come back negative. Is this normal?