All the numbers and math confuse me greatly. I need help!

Last period was January 29-February 2nd. My period was due February 27th. Tested positive February 28th. By LMP I would be 5 weeks this past Friday the 5th. Doctor said the gestational sac was beginning to be visible but I measured on track more with 4 weeks! And my HCG was right on track for that level too. I thought I ovulated the 13th (simply by app, nothing else).

My cycles are somewhat irregular & the doctor said I probably ovulated or conceived late! So by those calculations, when did I ovulate? It's all very confusing!