Can someone help me please?

Can someone help me please? . I went to a birthday party yesterday that was indoors. But I occasionally went outside. I wore 2 tank tops and a shirt which was a bad idea.. But it was pretty hot out yesterday. So I came home to find this rash on my sides of my stomach and kind of my back.. I don’t know if it’s heat rash or prickly heat maybe I wore to many layers. Or if it’s a form of hives but my hives never looked like this. I also have them today and they look worse.