I had abdo surgery 4wks ago. i woke up with pain in my neck/shoulder which i thought was from the gas. the pain is still quite bad and i have noticed i cannot feel temperature on my shoulder. my arm feels achy and kinds numb. what can cause this?

The symptoms are consistent with cervical plexus compression due to a prolonged and poor neck position but cervical herniated disc can't be ruled out. Massage or apply cold or warm pack at the site of soreness, take 2 OTC ibuprofen 200 mg (motrin, advil) with foods, every 6 hrs as needed for a day or two, move your neck and arm when pain has improved. Neck-shoulder-arm syndrome is usually limited.

You may possess an inflammatory immune brachial plexitis (Parsonage-Turner Syndrome), but not feasible to be accurate without a clinical examination. See a local neurologist and get this handled.