Pain in the left side of neck and arm and numbness of arm indicate cervical intervertebral disc syndrome where there is compression on nerve emanating somewhere in cervical spine is pressurised because of various reasons such as reduction in space, osteophytes or anything else. This will cause myalgia also. Treatment is management of proper intervertebral space to de pressurise the nerve. Medicines and heat can t address it permanently. Physiotherapy is useful. Yoga exercises are also helpful. Swelling in the back of head seems from some local trauma or lesion. No connection with cervical disc is evident in symptoms. Swelling should be managed locally by wait and watch. If it doesn t reduce, further investigations at hospital may be required to exclude any tumour, cyst etc. Hope it helps you.