My son has been very active in his life he is18 now he gets sick to his stomache when he plays basketball n sometimes has to throw up and gets headach?

Physical. Go see an internist and get him checked out - basic physical exam and lab work.
Emotional Factors. Find out what's going on in his life-girlfriend problems, academic difficulty, anxiety over school admissions, scholarships, drug use, etc. Hopefully, you have a regular doctor that can explore these issues as well as physical ones.