thanks for writing to HCM,
From the explanation that you have given it seems that you have a severe trapezius muscle spasm
. The bump may be your swollen trapezius muscle.
treatment options available at home without taking the help of a physiotherapist can be -
perform hot fomentation using a hot water bag on the painful and swollen area - for 15 mins 3 times a day for a week.
using very thin flat pillow while sleeping.
perform neck relaxation exercises.
later on as the pain reduces - start with neck isometric exercises.
for the initial pain - you can take any anti-inflammatory analgesic(orally or topically - over the skin)
if all of this still doesnn't help kindly see a physical therapist
as these problem if ignored can lead to cervical spondylosis
i hope this helps
wish you god health