When I was 16 I was very ill for several months. Initially the doctor diagnosed it as mono, but then she decided that my symptoms (especially dizziness) were caused by migraines. Interestingly, I didn't have any problems with headaches until I started taking the anti-migraine medication that she gave me, which gave me horrible headaches almost every single day. So I went to a headache specialist, who decided to put me on medication that was actually an antidepressant but in teenagers was supposed to prevent migraines. My mother was wary of the medicine because it was supposed to be highly addictive, but I was having such horrible pain every day that I begged her to let me try it. It did eventually stop the headaches, but I became very addicted to it (and I only had a very small dose!) and it took me over two years of struggle to wean myself from it. In addition, when I went to get birth control for the first time, I described my "migraine" problem to the doctor because I knew the pill had certain risks for people with a history of migraines, and this doctor didn't think the pain I was describing was a migraine at all but some other sort of headache.
I still don't know what was wrong with me, but the moral of the story is to be very careful with accepting diagnoses and especially with the medicine you take! I wish I'd researched it first--I did later and discovered that it's one of the most highly addictive prescription drugs in existence and the withdrawal process is miserable.