This sound like lymphoedema to me. Once the Lymph nodes are removed it is difficult for the lymph fluid to drain and this shows up as swelling. Initially this area is quite firm and hard, but over time it becomes a sort of baggy oedema.
Kris still has this 3 years post surgery. Some days it is hardly noticeable, others days it is more pronounced.
Some people see a specially trained Lymphoedema massage therapist to help. I think you are still in the early stages of recuperation and recovery and this will improve given time.
Tammy

Caregiver/advocate to Husband Kris age 59@ diagnosis
DX Dec '10 SCC BOT T4aN2bM0 HPV+ve.Cisplatin x3 35 IMRT.
PET 6/11 clear.
R) level 2-4 neck dissection 8/1/11 to remove residual node - necrotic with NED
Feb '12 Ca back.. 3/8/12 total glossectomy/laryngectomy/bilat neck dissection/partial pharyngectomy etc. clear margins. All nodes negative for disease. PEG in.
March 2017 - 5 years disease free. Woohoo!