LUMP UNDER MY DOGS SKIN, AND VOMITTING?

This weekend I found a soft lump , probably the size of a lime. She had been vomiting for a day or two also, I first found it by her ribs (where later saw a red irritated spot) then not even an hour later It had moved up to under her chin then up to her check, up to under eye and It went back to under her chin and it set there for a couple of hours but finally last night the lump disappeared. She's acting normal now and she's eating, "pooping" and peeing just fine, she hasn't thrown up at all. I don't have much money right now so I don't want to take her to the vet unless I have to. Does anyone happen to know what this may be?? It is severe enough to take her to the vet? I'm concerned. Thank you in advance to all answers.