conception

Okay, so I am 39 weeks and 5 days pregnant. Everyone and every calculation app is trying to say I had my last period in feb. But i did not have a period in feb. My last period was sometime in Jan. Now how does that work? Did i get pregnant in the beggining of Feb.? Cause if my last period was in Jan. my due date would not be Nov. 24th. I tested postive march 21 and i was just about 3 weeks and a couple days give or take. someone please help me understand this. Im so bamboozeld lol