I have a rash under my armpits, and it is spreading down to my stomach, i am not wearing deodorant and i've been putting vinegar and water on it. i seems to keep it from itching. what medicine should i be taking?

This : This is difficult to answer without a clinical examination so i would see a dermatologist. Possibilities include fungal infection, yeast, eczema, psoriasis, dermatitis (allergic), and other possibilities. See a picture of fungal infection and eczema and treatment options at the link below. I hope that helps!

Rash: You need to find out the cause of the rash, e.g., side-effect of medication, sensitivity to clothing, detergent, food, etc. Please see your doctor. Peace and good health.