For me, an hour after eating would be too soon to ride. In addition to the weather it could be that also, as you said you felt better toward the end of your ride. I've had the same thing happen if I tried to ride too soon after eating and it makes me feel queasy. If I take it easy I find that as the ride progresses I feel better and can ride stronger.

This happens wether it is warm or cold. So now I only snack before a ride and have a regular meal afterwards. If I know I want to ride in the evening I'll take a late lunch. For me the heat only exacerbates the whole thing.