HI,Good Evening.Thanks for your query.I studied the query in-depth.I understand your concerns.
With whatever facts told in your query,I would try to give most probable causes to help you to reduce your worry.
-By your description,its mostly of -Sebaceous
cyst on the back of neck with little infection and inflammation-may be by trauma or handling.
-I would advise to rule out the
Cervical spondylitis and
hypertension with Xry Cervical-Spine and physicians opinion, as a cause of the pressure to back of your head and neck.
-The infected sebaceous cyst could be a cause for the head and neck pressure.
-Excision
Biopsy after antibiotic /
NSAID cover would relieve you with this movable lump.
-You need not worry of the outcome as this-tumour is non-cancerous.
-Hope this would help to regain the lost-health fast.
-Wishing you early recovery and good health.Wellcome again.