Hi Caeley and welcome
I'm sorry to hear your hamster is unwell.
It does sound like your hamster may have Cushings disease which sadly is not curable.
I would go back to the vet and ask about this.
There is some information here that may help you treat this disease and compare to how your little one is. If there are dark patches with pigment on them it is almost certainly Cushings.
Cushings Disease in Syrian Hamsters - Hamster Central WIKI
Some pics here which may help too
Stages of Cushings Disease with illustrated pics (inc. treatment)