I am having the WORST week...first my guinea pigs had mites, then one had open cuts from the skin scrapings, and now I found a lump on my 3 year old guinea pig. The lump is about the size of a large pea. It is located in her armpit area on her left side. I just found it today and have made a vet appt for Monday. What could it be?? I'm praying that it is not cancer or anything life threatening.