Diarrhea is normal in 3 month old babies as their stomachs adjust to the quantity of fluids they intake. The colour of the stool is rarely a concern for doctors unless there is blood or mucous. I would suggest seeing your doctor only if the diarrhea persists for more than 3 days or your child develops a fever, vomits frequently, looks in pain or refuses oral intake.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.