He is a 4/5 month lop, had his vaccination and vet check yesterday at the RSPCA. he was in perfect health then, nut he's being unusually quiet and lethargis now, when usually at night he's hopping up onto the furniture and running around. he also has what feels like a small lipoma or other kind of lump under his left front leg. he seems to be eating/drinking/defecating fine.