Hi, I Have Had A Red Itchy Underlying Rash At

Hi, I have had a red itchy underlying rash at the top of my behind (specifically at the top of the crack) for over a year. Not a bid problem, just annoying. I went to the doctor and was told it was fungal and to use Lotrimin. It has gotten worse. It is blistered and is extremely painful and it has spread.
I have also taken meds recently for a fungal infection on my legs, which was from a mission trip and am currently finishing a course of meds for cold sores on my lips, but they still aren't healed with only two days left in a ten day course.
Help! I feel like maybe these are all related or affected by each other. I am miserable.
Thanks for your help.