Why is my 12 week old kitten throwing up often lately?

My 12 week old kitten threw up like 2-3 weeks ago it was a lot but a day after we took him to the vet he said nothings wrong he’s a great vet everyone loves him and a few days ago the kittens got their vaccines and the vet said they’re both good and to bring them in 3 weeks for booster shots and day before yesterday my kittens were on the bed and one of em the same one who’s throwing up got down on the floor and threw up under the bed I didn’t mind cleaned it up he was playing afterwards not looking like sick at all now he has this weird smell behind one of his ears and he threw up day before yesterday twice but today and yesterday and day before was quarter size white chunky puke sorry to gross u out but I thought maybe I’m over feeding them or it’s the tuna flavored food I did every thing and he’s still at it but very active throughout the day has someone had similar experience and should I take him to the vet thank u

Why is my 12 week old kitten throwing up often lately?
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