kim, given the headaches are one sided, it's almost a guarantee that the problem is related to your neck or back (unless you have one eye a lot worse than the other - and the headache would get worse as you used the computer and things)

i would suggest getting yourself to a chiro - it will be exxy for a while cos you have 12 years of history since the stair incident to work out - and your muscles and spinal allignment will be VERY stubborn and reluctant to move. you'll likely need at least weekly appointments for a while until the joint that is impacted starts to move properly. i was in a car accident in grade one and had headaches like you describe up until year 11 when all the "traditional" medical options were exhausted and i went to a chiro. it took a couple of months (i won't lie) to get to the point where i wasn't NEEDING the appointments every week, but i went from pretty much every day having a headache that was crippling me (not good in year 11) to getting a nasty one every 4-8 weeks. since being pg, with the relaxin, everything has fallen in a heap again and it's really nasty again so i'm back to weekly visits, but i'm able to stay on top of it most of the time and i know it's a short term thing

get thee to a chiro hun. get recommendations locally (you don't want a "bone cruncher" you want someone that also works with a physio if you can) - your injury may be related to muscle damage in your shoulder (i have that too - lucky me!) and torn muscle that hasn't healed, even though it may not hurt at all now, can link in to headaches as well.

good luck getting treatment - if you were further down this way i'd send you to Mark - he's my miracle worker! even a very "anti-chiro" friend caved when i hassled him enough - he'd been having headaches for years - and is headache free now after probably 5 years of them thinking he may have had a tumor due to the pain!