Is this Allergic reaction? Need Help

Here is the story. About 1 week ago I saw my cat's gum swollen then I brought her to the vet and the vet said she has gingivitis and requires dental cleaning then I said I will observe her first and didn't give me any meds then 2 days after that I saw pus on my cat's gums and I decided to bring her to other vet. My second vet said it is infection that her gum is swollen because there is a bit of hole that she might punctured herself with a small object. She gave me Antibacterial and Ascorbic Acid. Now It's been 5 days of taking her medication, her gums is ok now no more pus but I just saw today that the side of her lips is swollen it looks something like bitten by an insect. Is this allergic reaction to her medicine? I just read the the box of Ascorbic Acd and it has warning sign that causes allergic reaction to certain user, Is this the case or It might be something else? What to do about the swollen side of her lips?

I would call the Vet who prescribed the Ascorbic Acid and ask that question.  I think that's the best course of action here. 

It can make a difference whether the ascorbic acid comes in tablet or crystal form in a capsule with no other additives. The amount used can also make a difference. However, the extreme acidity of the supplement (and other factors as well) can cause a reaction no matter what. (Also, depending on the amount and length of time used, in some cats, just like in some humans, ascorbic acid can affect the functioning of the thyroid gland. So for certain individuals, long-term this vitamin may not be quite as safe as we would like to believe it is.)

I do agree with mrsgreenjeens's advice, you should talk to the vet who prescribed the ascorbic acid.

From my personal experience.....the first cat our family ever had many, many years ago, had some health issues for which our vet at the time suggested trying ascorbic acid. I still have the pictures showing a huge bald spot on our cat's face from the ascorbic acid tablets.

It took a while for us to figure out the connection but we did eventually and after the ascorbic acid supplement was stopped for good the fur grew back and looking at him later nobody would have ever guessed he had ever had a big bald spot there.

Since allergic reactions come in many (literally countless) forms from so many things, the first thing I would do is trying to find out whether the reaction you're seeing is caused by the ascorbic acid. The easiest way to do this (after you've discussed the problem with your vet) is stopping the supplement, watching for improvement and when there is significant improvement, starting it up again.

Ascorbic acid is vitamin C and cats naturally make all they need in their body - unlike us they don't need it in their diet.  If the ascorbic acis is causing a problem I would have thought it's the other bits & bats that are in the pill / powder that are the cause.  If the vitamin C itself was the problem then they would have a permanant problem since their bodies make it.

What I don't understand is why it was prescribed.