Ok firstly just go to your doc and they will either remove it there and send it off for biopsy or they will refer you to a dermatologist/plastic surgeon to remove it at the hospital.
I recently had a freakout as my GP told me he suspected I had a cancerous mole and in front of me filled out an urgent referral for suspected melanoma - I FREAKED OUT!!! I went to a plastic surgeon as my GP didn't think he should remove it, my pre-surgery lookover they identified 2 more that should go and then when I met with the plastic surgeon she looked at them and said that even with my history (remicade, methotrexate and phototoxic reaction) she very much doubted they were, people get new moles all the time and they can change its just what they do and rarely means cancer. She said my GP is just playing it safe. She did still remove them (just over a week ago infact!) as she said they could possibly become a nuisance but strongly doubts it is anything to worry about. I'll find out in a week or so if it was or not but I'm pretty positive after what she had to say.
My main suggestion is go to a doctor and get it checked/biopsied. Try not to worry until you get results! Stressing can cause all sorts of trouble with Crohn's. Majority of skin cancer is treated with surgery and regular check ups, even if it did turn out to be skin cancer you may not have to stop meds but may be a bit more likely for a recurrance (which I guess would be caught in the regular check ups).