so lately I've been feeling sick . like i don't what sickness though . because I've never honestly felt like this before . but when i feel sick , i start to get a bad stomach ache , then with the stomach ache i get a bad headache , then after i get a headache i get really cold , & sometimes catch a fever. sometimes when i feel that way , when i stand up i get really light headed , & feel like i'm going to pass out. also sometimes the light makes my head hurt too . i haven't really been eating good , or sleeping good because of this. what could these symptoms mean ?