3wks sore spot 4in long on back of head. Feels like bruise but not. Now in the middle of it iuarter size lump with fluid. Dizzy. Sometimes itchy/throbs.?

Fungal infection. A tender itchy swelling on the scalp that is new would likely be a fungal scalp infetion or tinea capitis. This needs oral antifungal treatment. A cyst or even and abscess could be possible. Time to see someone to check it out.