pimples on pup belly

She has a couple pimples on belly, nothing comes out when squeezed she doesn't itch either had 1 for a while but i just thought it was a blemish. Here's a couple pics, just feel like loose skin. Any ideas what it is. Like i say she's fine every other way but is in heat at the moment, thanks.

Apparently her nipples can get large during heats, strange how its only a couple swollen up. Never understand a female