What's wrong if kitten was spayed 2 months ago and now she has many lumps on her belly and chest up under the armpits and the vet doesn't know what it is and he wants you to watch it for 2 to 4 weeks?

She could have gotten an infection, or she could have been allergic to something that the vet used for the surgery. Also is the doctor sure that he got everything out? I know that they can leave in a gauze pad or something. They do that to humans they could also do that to animals. Good luck and God Bless:)