Constant lip and mouth ulcers after hospital admission over 6 months ago

Back in April of this year I was admitted to hospital for a really bad case of tonsillitis. This is after nearly being admitted for the same thing a year prior. I was on a few different types of antibiotics as I kept having bad reactions to them. A few days after being discharged I broke out in really bad lip ulcers which I had never had before. At this point I had maybe only had 2 mouth ulcers in my life. Since then I am constantly getting lip and mouth ulcers one after the other having never really dealt with them before.

I’ve been dealing with a few health issues that I’ve been going back and forth to the gp about. I’ve had lots of tests done for different things like certain auto immune disorders, my thyroid and I’ve had a few ultrasounds all coming back clear.

I am 23f, 5ft 4, 65kg and take no medications or smoke.

What could be causing this? It is due to all the antibiotics I had been on? Any help is greatly appreciated!