Question Concerning a Lump on my Kittens Side

Question
Name: Keira
Age: a little over five months
Vaccines:
-When we got her at the local animal shelter in December she recieved an 8 in 1 vaccine
at eight weeks
-When we took her to the vets office about a month ago she recieved vaccineS for rabbies and leukemia
Spayed?: Not yet. We are waiting to have her spayed at six months in June
Heat Cycles: she's in her second heat cycle, but has had no problems with it at all
Health Issues: None

Problem: I was petting Keira today and noticed she has a small lump on her side. It was not there yesterday.
Lump Description:
-Its on the side of her stomach
-Small (penny sized)
-Squishy
-Under the skin
-When applied a tiny bit of pressure, she doesn't react with pain or agony

Keira still plays, eats, drinks water and uses her litter box completely fine. I've never had a single problem concerning her health until now. She's even jumping from high places and acting like she usually does.

Do you have any idea what this lump is?

Answer
Pretty hard to tell when you can't see or feel the cat or the lump. My concern would be a vaccine related lump but they are pretty rare. Not the usual place for a VAC. (vaccine associated carcinoma)

If it isn't gone in a few days I would definitely have it looked at. Lumps on cats are not common unless they are an abscess, so this would be a concern to me.

Better to be safe then sorry. If it's still there on Monday, get her in to see your vet. If it starts to grow at all, get in her in sooner.

Keep her in the house, she is definitely old enough to get pregnant. I think 6 months old is the perfect age to get them spayed!