I'm not sure what method was used to determine your due date, but a due date of Sept. 21 means you conceived around Dec. 30.
So whatever bleeding you had mid-January was likely implantation bleeding or some other non-menstrual bleeding.
I'm not quite sure why you think your baby is small for 13 weeks - can you be more specific?
I know i got my due date 21st September :) meaning i conceived around 30th dec, i didn't have no bleeding? i just thought i might have conceived a little later in my cycle i just had a feeling due to body changes round about the 9th-10th i might have ovulated then but with the ultrasound confirming that due date i don't think there's really anyway i conceived around 9th-10th :) I was meaning if i did ovulate a little later in my cycle my baby would probably be measuring smaller and I'd be less weeks my right ? I'm sorry if I've confused you a little x
Oh goodness sorry I've totally confused you my last period started on the 16th-19th dec sorry x
First off congrats and breathe just relax eat good be healthy and everything will be just find don't get caught up in dates and etc sit back and enjoying being pregnant.::)