I'm Wondering Why I Perspire So Much When I Go

I'm wondering why I perspire so much when I go from outside into a store, or sometimes the opposite - from an AC cooled store to the outside. The outside temp doesn't have to be really hot. I am very overweight and do have problems with my legs. If I can sit down for a few minutes when I get into the store the problem isn't so bad. It's like my body has to acclimate to the temp. I'm post-menopausal.