my bitch has just had a litter. all the puppies have now gone to their new homes, the last one yesterday. Our dog is now trying to mount her again is it possible she is in season, she seems quite willing but is not swollen at all.

Unless she normally has a very short cycle (4 months between seasons), I would guess it's unlikely she's coming back into season, but would be slightly concerned that she might have an infection brewing as the smell of this can sometimes confuse males. Have you taken her temperature?

M.