There is this spot on the back of my head that aches. When I push it it hurts like a bruise. Is there anything to worry about or sinus related?

Painful spot. Sinuses are around the eyes. You have muscles in the upper neck that attach to the back of your head, and nerves in the neck and scalp. Muscles spasm and compression of the posterior occipital nerve can lead to point tenderness, sore spent in the upper neck, back of your head. Use heat, and neck massage. Pressure on the area may cause more damage to the nerve.