Mama, please bring your baby to the doctor or pediatrician soon, okay? A week of cough with phlegm in a 3-month-old needs a proper check-up to make sure everything is fine, I wouldn't wait any longer. I know it's stressful when baby's sick, but at this age it's really best to let the doctor assess him directly kaya don't hesitate to go. Sending you both strength, mommy!