What can I do to get rid of the rash on my legs? Should I take aspirin, ibuprofen or acetaminophen for fevers? Is diarrhea caused by HIV, my drugs or something I ate? What’s the correct daily dose of vitamin C? In April, POZ Partner will begin a monthly column in which experts answer  medical questions such as these from readers. No query is too complicated or quirky for our crack team. Send your requests to What’s Up, Doc?, POZ magazine, Box 1279, Old Chelsea Station, New York, NY 10113-1279. You can also e-mail us at docpoz@poz.com.