Damn it, I had written up a lengthy response to your post but I accidentally pressed refresh or something and now it's all gone
Anyways, thanks for the reply and here's some more information:
The MRI was ordered by a family doctor who didn't know whether or not the headache was actually sinus-related.
I had similar headaches 2 years ago and instead of going to an ENT, we went to a neurologist at that time. (Again, we didn't expect it to be sinus-related). After diagnosing it as a sinus infection, I was put on one course of anti-biotics and the neurologist never followed up again or referred us to an ENT.
This time, my ENT put me on 500 mg of Biaxin (twice a day) for 3 weeks. In addition to that, I was taking Sudafed, Allegra, using a neti pot daily, and used a nasal spray for a few days. After about 3 weeks of that, I had felt fine and it was to the point where the only medicine I was taking was Allegra once a day (the doctor prescribed Allegra after a blood test confirmed that I had allergies and he thought that might have been the cause of the infection). So after taking that course of treatment, I felt perfectly fine for about 2 weeks until the headache reemerged. The headache has been there constantly for the last 2 weeks. It comes and goes, and varies in intensity (although never as painful as before), but the fact that it is still there concerned me and my parents.
After about a week of thinking about it, my parents and I decided that we would like to have surgery if it wasn't too risky. We didn't want to take the chance of having the infection/headache coming back all the way (at it's worst, it was so painful that I had to miss some final exams at school and I also went to the ER one night).
We discussed it with our ENT last week and he said that personally, he would try a more conservative approach if he were in my shoes (continued anti-biotics, more nasal irrigation, etc.) but that if we really wanted to, he would be fine with doing the surgery. In his opinion, the best option would be to continue more anti-biotics, etc. but surgery was still a good option. So at that appointment (July 15th), my ENT scheduled the surgery for July 27th and he also put be back on Biaxin. So I've been on Biaxin and been doing nasal irrigation for the past 7 days, and the headache has not subsided at all.