What Causes Buttock Area Rashes With Odor?

I have a 1 year old who has what seems to be a rash in her diaper area but i have never seen one quite like this before. It doesnt seem to itch or hurt her at all but it looks like little red pimples covering her entire diaper area. I first thought, food allergy, but she hasnt had any new foods lately. She also has always had this very strange smell that you notice even when she isnt wet. It almost smells like amnonia sometimes. I have no clue what this could be from and the doctor we have seen hasnt really said that is it a concern YET. I am just wondering if maybe it could be some sort of STD or something.