Due date questions!!!!!!

Soooo back in December I lost a baby at 4-5 weeks.... (Supposedly) my last period was November before thanksgiving.... I ended up bleeding out completely on Christmas Day. By January I was confirmed Pregnant again... Jan 18 they said I was 3 weeks along.... But I either did not lose the first baby I was pregnant with in November or it was a twin and 1 baby survived because my sister who already has a set of twins.... Went thru this with her 2nd set.... Only 1 baby survived at 8 weeks. I am told my due date is September 29th but I was told at a prior sono at a hospital it was actually the beginning of September! I also feel the baby is further along compared to my other two pregnancies..... Am I going crazy??