make sure your on a strong probiotic to replace the loss of good bacteria so you dont end up with a full candida infection. Since your working with a doctor you could ask him/her for VSL-3 help your body.
blisters could be from the bactrim since it is a sulfur drug or it could be due to the die off of many species of bacteria in your body. Antibiotics cause die off reactions in the body..
Keep in mind allergic reactions that you see on your body could be from a earlier reaction that you had to the drug.