What Causes Thick, Red And Inflamed Skin Under Armpits?

My son is 28 years old and has Down Syndrome. His height is 5 ft. tall, weighs 194 lbs. He has thick skin in his armpits and at the present, the skin looks irritated, red and inflammed. The dermatologist appt. is not until 8/19/11. I am very concerned as to the length of time before the appt. It seems as if there is an odor now. He is presently taking Minocycline 100 mg. 2X a day and has been taking this medication for approx. 3 months. What do you recommend.