What can your dog have for leg pain?

Yes that's why dogs lie down in the sun!

So you should call them in and check.

That's for like when they get hot. I think you mean when they are ready to mate. If that is the case, no, it is not usual for their legs to ache. They might ache when she is pregnant because of the weight of her puppies, but that's beside the point. Hope this helped! :)