I have brown like spots on my stomach, back, and legs, they just came out of no where, I usually have heat rashes which are red/pink, but these ones are a brown color they don't itch, or anything then I have bruise like marks under my arms. Can anyone help me I've looked everywhere for information, and can't seem to find anything...

You'll have to see your doctor. There's absolutely no way to give you a diagnosis over the internet.