Feeling sick all the time, clammy headaches, pains in my head,what could it be?

I get pains in my heads all the time sometimes they can get really painful where I have to sit down for a bit. I've always got a clammy headache all the time and I feel always tired, I feel sick all the time and most the time I go to throw up but flem just comes up but just now I was actually sick. Im really sensitive to light and sound and my muscles ache alot. I feel weak all the time. Once I collapsed but I thought it was just the heat could it be linked?? This has been happening alot and Im only 15.