I have constant headache and I don't know why

I've had a headache for three months now, It's especially bad in the morning and in the evening. I was to many doctors by now and nobody could tell why It's like that, I had many tests done and took many medicine by now and I'm just tired of it all. I barely can go to school since it's so painful, even if I take painkillers they only work for about an hour before the headache returns and I can take only one pill every six hours since they are strong and easy to overdose. I tried many things to get rid of it but nothing seems to work. I just want the headache to go away so I can live like I did before it started. My head hurts every single day and the only relief I get is from the pills which like I said don't work the best. I just want it to at least hurt less.