My calves are having random hotspots, that come and go. They don't hurt, but are just are hot. What can this be?

Interesting. Hot areas that come & go without pain makes one think of hives, which can have multiple causes, but these don't just occur in the calves. Burning discomfort in a calf area could indicate a nerve condition, however it isn't usually felt just in the calf, & wouldn't usually involve both calves. If symptoms continue, best to see your doc who'll be able to look at these and ask you more questions.