
Hi, well done to get her to 12 days, 123 g is very small for a pug of this age, but I have had them this size at this age (and older - one was 4oz at 4 weeks) who have pulled through. If she is gaining steadily it sounds promising. With pups this small, even at 12 days I still treat them more like a newborn and keep them on 2 hourly feeds as they simply can't cope with longer gaps. I try for 5ml per feed which works out at more than she is taking, but again, if she is gaining then it sounds like the amount is OK.
I don't have any experience of the wet rear end problem, and would go with the advice others have given and get her checked at the vet.