There is no reason you should have to suffer like you are suffering now. You might want to do a couple things.
1. Ask the oncology staff for printed information about the drugs you are taking. Look on there to see if rash or skin reactions are listed as a possible side effect.
2. Do an internet search on each drug and look up side effects.
3. Get the name and phone number of the drug companies for each drug you are taking and call them.
You can get phone numbers by doing a search for the drugs name. That will reveal the name of the drug company that makes the drug. Click on that link and go to the drug company website. A phone number and other contact information will always be listed somewhere on the website.
Most drug companies have pharmacists who are willing to talk to patients about issues and/or side effects they experienced while on their drugs. I have found them very helpful each time I did that.
4. There might be some kind of drug interaction between the drugs you are taking (both cancer and non cancer drugs) that might be causing the rash. There might also be an interaction between one of your drugs and some kind of food. Your doctor may not even be aware of this possible problem.
An experienced drug company pharmacist might be able to tell you about that.
There are various websites where you can check for number 4 yourself. I have included links to 2 of them below.
http://www.drugs.com/drug_interactions.php
http://www.medscape.com/druginfo/druginterchecker
I had this experience a couple times. Once I found out there was an interaction between 2 drugs that my doctor was not even aware of. After I talked to a pharmacist I was able to follow his advice about taking the 2 drugs at different times of the day to eliminate the symptoms. It was very simple to solve that problem once I knew how to do it myself. I told my doctor what I did and he was happy to learn something new he didn't know before.
Good luck. Take good care of yourself.