drooling and loss appetite

[sophie13]

my angora female cat, 1.5 years old, was drooling about 5 days ago. she also lose her appetite. 2 days later, I brought her to a vet and they found some inflammation on her gums. they said that probably the symptoms caused by the inflammation or maybe kidney problems. (in addition, she always drooling if I give her vitamin gel or any oral drugs.)
they gave 0.1 cc im injection of dexamethasone and anti-hypersalivation, twice a day. They said I have to inject it for the next five days and if after it, she's still drooling, she has to undergo some blood test to precisely know if there's some kidney problem or not.
But, I stop the injection on the 2nd day and till now I haven't given the injection. but from my amateur physical examination, I think there's no more gums inflammation cause the gums isn't red anymore and I think the appetite almost back to normal. but she's not as energetic as usual. then, if I look at her urine, there's nothing wrong with it, nothing foamy or anything. so is the faeces, no blood or anything.
do I have to continue the injection? is there any complication cause I suddenly stop it?
and from your medical view, is there a possibility she has kidney problem? should I brought her to undergo blood test? should I change the food with the fewer protein? and is that ok if I dont change the food cause she doesn't want to eat except for the usual food?
please help me, I really worried about her. thanks for your help.