The skin on my biceps is red and inflamed with little tingling bumps. i wore a cotton shirt all day that i've worn before. what should i do?

Cool it down: Your shirt might've had some sweat on it, inadvertently, you've may have just irritated to the skin there, especially if yours shirt is tight. Make sure the area is clean that you've washed it was soapy water, and then cool it down with a cool pack. That'll reduce the irritation pain, and swelling or inflammation. If it gets worse, then call your doctor, as s/he will have to see it in order to treated effectively. S/he can recommend a cream that you can use to help reduce the painful bumps.

Skin rash: The skin rash could be from a variety of causes. The description is vague and with a photo it is difficult to characterize. If the rash persists or increases then see a dermatologist for evaluation and treatment.