Increasingly itchy rash for 6 mos all over body w/ concurrently increasing constipation (< or = 1 bowel movement/week now). i'm very hydrated.

Not enough info: If you have had a rash for over 6 months, you should consult a dermatologist to find out the cause. As for the constipation, it may be caused by taking too much antihistamine to control the itching especially if they are of the sedating type (benadryl, atarax (hydroxyzine) etc). In the future, provide more details on your health status (other illnesses, medications taken etc) in order to get a better answer