Im not sure if this is the right place to post this because its not entirely acne related but skin related, but i have no where else to ask.

I have had really bad acne for a few years and been on many meds, and finally im on isotretinoin 10mg for past 3 months however it hasnt helped, its gotten worse.

And a few days ago, my armpit developed a large rash, that looks like acne or a rash. And is extremely painful throughout the entire day . Each day it keeps getting worse, and this morning i noticed the rash or whatever it is is progressing farther down my body and getting worse.

I am worried, and wondering what i have/what is wrong, and what i should do. It hurts immensly.