No that's no a sign of labor. that's just a sign of pregnancy. Headaches start from day 1 and usualyl last until the end. I'm sorry to give you bad news i'm sure you're uncomfortable, and being overheated is completly normal. Carrying extra weight is a bit of a workout and can leave you out of breath and hot. Try taking a cool shower, and eat ice cream, or popsicles. Something that'll smooth your stomach. Good Luck!