My Son Is 11 Years Old And Has Had A

My son is 11 years old and has had a series of symptoms over the past month. First he had a stomach bug, vomiting one night and with serious nausea for about a week. Then he has had nausea off and on for about 3 weeks. This past few days he developed a headache. His white blood cell count is normal, he has tested negative for anemia and we just tested for Lyme which was negative. He has also had a rash over various parts of his body, mostly upper torso and upper arms. The rash tends to come and go and can be itchy. He also had a rapid strep test which was negative but he is going back in for another strep test tomorrow. Any thoughts? Thanks.