What can be the cause for pain in the right axilla, constant numbness in the arm? Worsens during sleep.

armpit pain, especially if accompanied by an axillary mass, usually associated usually swollen lymph nodes under the arm. Other possibilities include a lump on the skin that appears under the arm as an infected skin follicle. Other causes are less frequent. When the pain is accompanied by numbness of the arm, as usual there is a sensory nerve involvement at that level, the most common causes include a physical nerve injury (eg a nerve entrapment), or a disease that affects the nerves (eg neuropathy).
Because of the possibility of serious diseases that can cause these symptoms, come early for an assessment by your doctor.