Hi...I'm 21yrs and I have a complaint since 2yrs. I get severe headache and become forgetful.?

My left and right sides of head aches when I think a lot or during exams and interviews, due to which I can't concentrate on what I study.Head-ache stays for a coupla days, though I take rest.Sometimes, it is accompanied by giddiness.I first thought it might be due to exam stress, then it repeats whenever I go out in sun, though its jus just awhile. And now I'm becoming very forgetful, I can remember only those things that I write down in things to do list.I forget simple figures the next day itself.I sometimes can't pay attention to what people say, though I feel I'm listening carefully. I can't take more than 3-4 intructions at a time. For exapmle, if anyone gives me details about finding an address, I fail to listen and comprehend directions completely,I can take jus2 or 3.How much ever I try to remember, I forget the lessons I learnt last week.I can't remember anything I study from the previous semester.Does that mean I have a neurological problem, or is it just lack of IQ?