I assume you had intercourse in March also, and are just trying to rule out February 16? If the doctor gave you the estimated due date based on an ultrasound, you can rule out February. When was your last period? Presumably you had one between February 16 and mid- to late March? That would also suggest you did not get pregnant from the sex in February.
I'm 6wks 2 days my due date is December 18th conception was probably around march 22ish. I hope that helps