Welcome to the Migraine Board. I'm sure you will find useful information from the experience of fellow suffers, as well as a lot of support.
Personally, I've had Migraines since age 8, diagnosed at 13 years old, and have run the gambit of all anti-migraine medications since then. Because I've been such a hard to treat patient, I have been selected from a very scarce number of qualified applicants to participate in a clinical study at the Medical College at the University of Virginia. So, basically, BEEN THERE, DONE EVERYTHING.
It sounds to me that you originally started out with a migraine, but did not get suitable treatment at the beginning. I think now that it has lasted all week, you have thrown yourself into a REBOUND headache situation. This happens when you take too much medication, either prescription or Over-The-Counter medication. Medicine for treating migraines should not be used more than two days a week. You didn't mention what OTC medication you were taking or how much, but clearly this seems to be a new problem for you.
Head injuries usually don't cause migraine attacks. Usually there are a number of different conditions that can trigger an attack. A migraine can have triggers beyond your control, like a sudden change in weather or temperature, hormonal changes, bright light, loud noise, eye strain, etc...Then there are food triggers like aged cheeses, red wine, nuts and many others. THe good things about these triggers is that you can keep a food diary. The only way to find your triggers is to write down what foods you ate prior to the start of the migraine attack, and note other condition, like environmental or hormonal.
Start keeping your food diary right away so you get in the habit of doing it so you can see any longterm patterns. Other than that, I would head off to the local ER (have a driver) so that you can get a pain shot and get rid of this headache. Dilauded and Phenergan is a good start.
Let us know how you are doing and what treatment you received at the ER.