22, 23 or going on 24?

Those are the confusing numbers of pregnancy. See if you can follow along. If you go by the pregnancy calenders, i am starting my 24th week tomorrow (weeks in pregnancy always start on a saturday). Ok, 4 weeks ago at the dr I went in as 18 weeks, then they told me I was 19 by the end of the appt. Ok, here is the duzie...I went on wed for my month check up, and besides the baby being super sutbborn it wouldn't show us if its a he or a she, but besides that, i am now only 22 weeks. Is my OBGYN in a black hole time warp? I am so confused!!!!