What Causes Raised Red Marks On Body And Fever?

Hello. My 10 month old baby has little red marks, some raised, some not, since a few days. Most only on her upper legs and bum, a few on her face, back and tummy. She had a low grade fever a few days ago, just for a few hours, and 3 runny stools in her nappy. Next day she was totally fine, she ate, laughed, slept well. Only thing she has is these red spots. Any ideas ?