how old is everyone? and how far along? im 24 and 17 weeks 🤗

Im having twins a boy and a girl its my first pregnancy im 4 weeks now

23 weeks im green

So i get how 40 weeks is 9 months of pregnancy cuz not every month is exactly 4 weeks but im confused how its divided. I got pregnant the beginning of may so the last week of September ends up being 20 weeks which is 5 months (may june july aug sep) but im confused how the last 4 months (october, nov, dec, jan ) also ends up being 20 weeks cuz how does the first 5 months equal 20 weeks and the last 4 months equal 20 weeks cuz im due beginning of february.

im 14 weeks but im not showing is that normal