Why does my stomach feel off all the time?

ok so my stomach feels off alot, like nauseas, or fluttery nervous feeling (which could just be me scared of actually getting sick) We went to the doctors for allergic tests and im not allergic to wheat or dairy, but my thiroids i think is how its spelled? are enlarged or something like that, and i have this gag feeling in my throat all the time, like the feeling you get right before you get sick,and i can get grossed out alot. Ive never had a very sensitive stomach but when i was nine i had the flu and afterwards i remember i went through the same thing im going through now for like a year, and now im fourteen and i got the flu again and i feel gross again. so i pretty much have the feeling of like the morning or day after the night you got sick where you're not actually puking but you feel off and you get grossed out and gag easily. its super annoying and uncomfortable and id rather not ender another a whole year of this so if someone could please give me an answer, or something to help when it comes to make it calm down would be REALLY appreciated (: