My russian dwarf hamster has a lump on the side of her face by her ear !!?

she has gotten a lot skinnier and we did take her to the vet and they gave her some stuff for it and she got a wee bit fatter !! so we thought ggod shes better but then today, we noticed she had a lump on the side of her face and just thought it was food but its rather large and its round and hard and im not sure wot it is, but i think it might be a tumour and we are going to take her to the vet again !! i am realt worried but expecting the worse !! :'( wot do u think it can be ??