21 weeks or 23?

so even though I'm not really showing I do have other symptoms of being fat. so anyways I have the worst memory before pregnancy now asking me anything is pointless. so idk how long, I have just found out today that I have been putting my baby 2 weeks in advance. at 21 weeks today 2/19/18 I swore on everything I am 5months 3 weeks but in all actuality I am only 5months 1 weeks..... has anyone else have this problems?