So sorry you suffer from headaches. I would look into getting your teeth checked as other members suggested.
As far as the codeine. Well this is very personal, but if it can help you, or anyone else, I would like to share. When you mentioned you were afraid you might be addicted it struck home.
Opiates and opioids (codeine, oxycodone, oxycontin, hydrocodone etc.) are very, very addictive.
I was a functioning addict for many years, meaning I went to work every day, paid my bills, had my kids looked after and dinner on the table, clean house and animals taken care of...It started with a back injury. I took 5mg of percoset occasionally and within one year was taking 10mg up to 7 or 8 times a day. I took that high dosage for over 5 years. For many people, tolerance builds up fairly quickly, so it takes more to get the same pain relieving effect as a lower dose had in the past.
Also, for many people (like myself) opiates give you an almost euphoric feeling, or bursts of energy, and because it masks pain you never will truly heal properly if you don't allow your body to rest. When the medication wears off, the pain returns, sometimes worse if you re-injured yourself without knowing because the meds dulled your pain and you over-did it.
With a headache, it could very well be withdrawl related if you take them like clockwork.
If you have been on the codeine for a long time, and do not wean off of them slowly, cold turkey detoxing is heck and can be life threatening.
Opiate addiction is no joke, and once you realize you are addicted, it's frightening. If you already know all of this, please forgive me. I'm not trying to be a know-it-all.
Please, please do not take this as "preaching" or "scolding" ... I absolutely am not intending for it to be. I do suggest, as someone who has been through the whole pain meds, addiction, detoxing rollercoaster.... to talk with your doctor.
I have a bottle of liquid Vicodin here for emergencies, and it's a fight with myself every single day to not take it for every ache and pain or when I "think" my back, knees, shoulder, whatever is going to hurt.
Big hugs, and if you ever need to talk and for someone to listen, don't hesitate to write to me privately. You will not be judged ((hugs))