@SteamLouis-- You know what, that's actually possible. My dad had red man syndrome because of vancomycin antibiotics. Thankfully, it wasn't very serious as he stopped the medicine right away. His doctor switched him to another antibiotic.
You still need to get checked out and get all the tests requested by your doctor though. There are other, more serious causes of the condition and all of it has to be ruled out before it can be diagnosed as a drug allergy. Now that you've stopped taking that drug though, if your symptoms lessen and go away on its own, it probably was the drug causing it.