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Pain and swelling in arm can be due to either venous pooling or due to lymph pooling. Vasculitis, thrombophlebitis and lymphangitis should be ruled out. The other possibility is deep vein thrombosis. You should check your under arms and breast for lumps. Please consult your PCP and try and get a referral for a vascular specialist. Also fix up an appointment with your gynecologist (if you are a lady) for breast examination.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!