First of all with Epilepsy you you should be going to see a neurologist as well as a primary care doctor.
Personally I would be more concerned with staying on Dilantin for such a long period of time. Although an allergic rash is a possibility it would be very very unusual and if it’s Steven Johnson syndrome you’re concerned about as I said in another post that 0.04% probability and also there are DNA tests that can be done to check and see if you may be allergic. Also get a vitamin D level. If you do in fact get the vitamin D level checked I hope you will share your results although I am 99.9% positive you’re low and if I were you I would start a vitamin D3 supplement ASAP. Although I probably wasn’t supposed to advise you to do that I feel it’s more important to give you that information than to follow the rule in this particular case.