Generic Manufacturers

Hey everyone, new here. I will try to keep this short. I had been seizure free for about 11 years. One day last year when I picked up my medication the pills looked different. I questioned the pharmacist and he said "it is the same thing, they just changed the color of the pill". At that time I had no clue about different manufacturers. I know, that seems a bit stupid. After about a week of taking the "new colored pill" I had a seizure. That is when I found out about different manufacturers. I called my Dr., and I was so angry. 11 years seizure free down the tubes! He said he would make sure the pharmacy gives me the same manufacturer every time. Last week the pharmacy told me my manufacturer is having a backlog and they don't know when it will come in so I would have to change. Last time it was changed I had no idea anything was changed so my seizure wasn't brought about by stress or negative feelings. This time I feel fine except for an awful headache. It started the evening that I switched and it has been 4 days now. Is it possible that the same medicine can give different side effects based on the manufacturer? I'm worried this is all in my head and a "nocebo" effect. I keep trying to tell myself everything is exactly the same.