Why do i feel like trowing up when im outside?

idk why but every time im outside helping my dad with the fence (usually at morning tru afternoon) i feel like trowing up and i get tired really fast.And i just feel like sitting down i mean i don't do that much i just give my dad nails why hes hammering them in the fence so that's like just standing there and im 13 and i don't think there's a problem that i have or something?And im going to disneyland in 2 weeks so im scared that if that when i walk im gonna feel the same why (trowing up)And not able to go on rides please help