Please read and help

So on 12/08 I got a BFP then on 12/09 I confirmed with a digital test. 12/11-12/14 I had spotting/bleeding ask j just accepted that I had a chemical pregnancy/miscarriage. I went to the doctors 12/14 and was told my pregnancy test was negative and that they think I did in fact have a miscarriage but they would schedule me for an ultrasound. They did blood work but I never got the results back and I never went to my ultrasound. I just accepted the loss and moved on.

Well today 12/27, I randomly decided to take opk test and pregnancy test and both came out very positive. I took two more pregnancy test, and one more opk. Same results. I counted the miscarriage bleeding as AF so my calendar says my fertile days are 12/20-12/26, Ovulation date 12/25. I had sex 12/15 after the bleeding stopped then again 12/20, 12/21, and 12/24. Is this just left over HCG, but if so how did I get a negative result before and now such dark lines that came instantly? Did my clinic get my test wrong and I never had a miscarriage? Or is this a new pregnancy?