I banged my head off and on for 45 min. should i be concerned that is still hurts 2 days later even after taking 3 advil (ibuprofen) can't lean my head back.

Yes: I am always concerned if an injury is not improving. On the one hand, it may just be sore muscles causing your pain, but if you were banging your head really hard you may have injured the spine or even displaced a intervertebral disc - though less likely. If it is still stiff and sore i would recommend seeing your physician.

It depends: The reason for your head banging is not clear. If riding something that jerked your head around and banged it against something, you most likely have some neck muscle strain. The second day after is usually when the most stiffness and pain but then improvement from then on. Advil (ibuprofen) is helpful for about 6 hours each dose, then must be repeated. See doc if not better in 3 more days.