Talk to Pediatrician on Baby Having Small Spots

AoA My daughter is 9 months old. She had fever few days ago. Doc recommended antibiotic. But on second day of giving antibiotic she had red spots all over her body. I stopped giving the medicine and spots disappeared. Now toaday she again had spots only on the exposed parts of her body i-e legs, arms, face. Which are sometimes darker with swelling and other times very light. No other symptoms. But she is teething. Now i am confused Is she allergic to something? If yes how can we find out what it is. I know it is not food related because i didn't gave her anything new. If its not allergy what could it be? Kindly guide