False postives?

So i have had 2 pregnancy scares in my life last year around this time and took seven tests (of different brands, types, and times of days/weeks) i took seven because i was in-denial. They all came back postive doctor said I wasn't pregnant. Fast forward to about a month ago i had the same thing happen. I had all the symptoms missed period and all and took 5 tests (in the same way i had last time varying in different times and types) they again ALL came back positive and again doc says no baby. I was tested for all sorts of different things from blood tests and std tests everything came back fine. So why am I constantly getting false positives? I tried asking my doctor but it was my first time seeing this doc and she was completely snarky and rude and refused to answer my question or look into it. So any theories or ideas of why this keeps happening?