Sounds like a typical vet analysis for a small animal really unless they knock the animal out and do a proper assessment.
Really do hope the antibiotics start to kick in if this lump is infection. Did the vet say give it 7 or 14 days and then go back?
If she`s managing in herself rosie it`s all you can do for now really and give her love. I saw an emergency vet one Sunday with my female Chinese (couldn`t urinate and was passing blood). £72 later, I came away with a small bottle of Baytril. She died during the night. Makes me wonder if these vets even do enough sometimes when it`s a small rodent. But then they are small and delicate to so the risks of surgery there. x