Tiny hard bumps all over cats belly

I just noticed my cat has tiny hard bumps all over her belly, and they are not on the top of her skin, they are under her skin. She had gotten fixed, and is eating a different brand of hard food, she's about 5-6 years old. What could be wrong with her? I'm honestly afraid, is this a sign of cancer or could it be some sort of allergic reaction to the new food she's on? I just moved to Kansas, and had not noticed such bumps untill today at 7:21am.

Thank you so much for the replies, I really appreciate it. She's got a vet appointment on monday, though I am a bit tight on money atm. I just purchased two budgies, and a hamster for my husband. And the rest we need to save for rent and gas. I think we're good, as long as the physical exam and treatment doesn't go over $100.00. She used to eat alot of Friskies wet food, and I don't know what dry food she had, being I never really saw the packages my friends mother bought. I lived with my friend and his mother while my husband was at basic. We've been in Kansas since the 5th of october, and have started buying the dry food Pet Pride Indoor Formula, and I suppose that answers the question about her being an outside cat. She's been an indoor cat all her life, she just got spayed a little later then she should have, do to budget issues.

I guess hives under the skin makes sense, but I've never heard of it before nore have I experienced something like that with any of the animals I've owned in my life. Shorty is special to me, so when something ails her, it bothers and hurts me too. I've had her since she was a new born, and my bond with her is really strong.