Hamster mouth tumor or abscess please help

[Renss23]

My hamster is a syrian boy nearly 2 years old. In the picture attached is what he has been going through in the past 2 months. I have taken him to THREE different vets in my local area in the desperate need to get him help. All of them gave me antibiotics and none of them worked. Due to this they said it is probably a tumor. However if you look at it ... from what I have read online it doesnt look like a tumor as it is red and looks like an infection. It does however grow very quickly. I dont know what to do i run out of options all the vets tell me the same thing !! I have been feeding him baby food that has safe ingredients for hamsters because he cannot eat his hamster food anymore.