Hello, i have a very sore lump on the back right side of my head. it appeared yesterday from no where and has not stopped hurting, should i be worried?

Likely a lymph node: Lymph nodes can develop around head and neck area as a response to some infection or inflammation in the surrounding tissues. Sometimes superficial skin infections or even dandruff or lice would be enough. Take some ibuprofen (400 mg) thrice a day for a couple of days. See your GP if it doesn't resolve within a week or so. Good luck:)