It seems like you have contracted a fresh upper respiratory tract
infection from the house-boating trip. The hard lump behind your ear/upper neck may be an enlarged lymph node
due to the on-going infection process.
I would suggest you to be examined by an ENT specialist
. You may require a course of antibiotic like Amoxicillin
Do salt water gargling with warm water twice a day for a week now. Take simple anti-allergics like Zyrtec 10mg at night for 2 to 3 days. Also, Tylenol in case you have or develop fever.
Get well soon.