confused about lmp....

Estefani
Has this ever happened to anyone? So on August of last year I had 2 periods in a month. One started on august 1 and the other on august 28. On September I missed my period and had a positive pregnancy test. Today, it hit me and was thinking if I should've gone with the first date which I had my last prd or the second date. I've told my doctor that my last prod was on the 28th of august. I'm 26 weeks and 2 days estimating from the 28th but if it's not the correct date I would be 30 weeks by estimating from august 1. I don't know I'm so confused. Which date do y'all think I should've told the doctor? I've also been feeling the baby pushing down on me and that has happened to me the last weeks of pregnancy.