What would cause a itchy rash on the right side of my stomach and chest?

One sided rash. Shingles can cause a one-sided itchy rash. See your dermatologist for an evaluation.
Many possibilities. There are many things that could cause a rash. Several types of inflammatory conditions of the skin, allergic reactions, and sometimes bacterial, viral or fungal infections can cause rashes on the skin. Insect bites can also be the cause of a rash on the skin. Have it evaluated by a professional and get the appropriate treatment.