BFP and Confused

So, long time app user first time posting. I've been TTC for 8 mos after getting the all clear after beating cervical cancer. My cycles have been 28 to 38 days...so inconsistent. Last AF was 1/24. App says next AF is due 3/2. Was using clear blue ovulation kits. They were low at first and not consistent with the app. Then I had 7 days of high and a peak on Wed. 2/21 and had sex. I had small bleeding right after and it scared me. Haven't had that happen before. It was only once and clear CM since then. My boobs started to be really sore last week and have continued. Too soon for my PMS symptoms. I don't know why but, I took at HPT and it was blantently positive! So, I took 4 more and all BFP! I am excited, but can't believe it's true! My science brain is like, but how?!? I'm thinking my OPKS were high because of Hcg. I read that can happen. I have an appt for a blood test on 3/2. Crossing my everything that this is true!! Thanks for listening! - J