Reaction to medication I’ve used for a long time

I’m just so annoyed. I’m suddenly reacting to a medication I’ve been using for over a year. It seems like it came out of nowhere. It’s definitely the med, not anything else. This was a very important med for me too that helps with symptoms from one of autoimmune diseases. This isn’t the first time a med that had been perfectly fine suddenly caused a reaction. I’m just so sick of this.