Help mamas!! So scared

Mommy

Hey ladies I was just wondering...is the first day of a MC considered first day of LMP? just asking because I cannot figure out how far along I am due to lifelong irregular periods and two recurrent miscarriages right before this pregnancy. The last time I bled was from my MC 12/19-12/24. Didn't get a period before I tested positive again around 01/17. Anyone that can make this make a little sense. My US yesterday showed just gestational sac and yolk sac but I'm thinking I'm not as far along as they think. I think they used my MC bleeding as a lmp and just estimated based on a 28 day cycle which I've never had. Cycles before the mc lasted anywhere from 32-43 days. PLEASE HELP 😓 Praying to see healthy peanut at next appointment 02/23 🙏🏽