red itchy bumps on my butt and thighs ?

Hi, welcome to the ehealth forum and I am glad to help you.
You seem concerned by the red itchy bumps on butt and back of thighs and on forearm for about 2 weeks.
You must consult your dermatologist for definitive diagnosis though there seems to be the possibility of some allergic reaction which is manifesting as rash/hives. Hives are raised, often itchy, red welts on the surface of the skin.
The common triggers are medications, foods (shellfish, fish, nuts, eggs, milk, and other foods), pollen and insect bites.The other possibility is of eczematous reaction but the definitive diagnosis is not possible online.
Hope this helps. Take care.
Note: This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.