Hello! My five-year-old chihuahua, Margie, has this lump/rash/bruise-type thing on her belly. I noticed the slight discoloration a couple of days ago and the lump last night. She hasn't changed dog food, been around any new dogs, or been outside anywhere different than usual. While she has been licking around the area, it doesn't seem to be bothering her more than slight irritation. Any ideas what it could be?