I have pain in my right arm pit area and there is also slight swelling so what could it be?

Need to be checked: Painfull swelling is often caused by an infectious process. In your arm pit/ axilla it could be a benign (non cancerous) lesion like lymphnodes, cysts of the skin, fatty tumors and developing abscess from an infection. It also could be a cancerous lesion. If this is not resolving within a few days you must have your doctor check this out.