I found a small lump on my dog's shoulder area that has like a brownish head in the middle. It has been there for weeks, did not grow in size and she has not been irritated by it. It is also not pain when I touched it. She's an 11 year old female Chihuahua. Anyone has any idea what it may be? I will be checking with the vet soon but would greatly appreciate any opinions first. Thank you!