Hello
Seromas can take quite a long time to resolve. I have seen it take weeks. Or even 2-3 months. The key is that it is never bothering your dog and never shows any signs of being n infection.
In my experience it just has to reabsorb on its own and on its own time.
Hello,
If you have not been to the vet already ( I always advise going within the first three days of having a new pet) then YES! Depending on the severity of the diarrhea and your puppies overall attitude this might even be an emergency. If he has had multiple episodes of diarrhea OR is not playful and seemingly happy then you should go now. Of particular concern is parasites and parvovirus.
Your puppy should be seen within the next day IF the diarrhea is NOT severe and they are acting normally.