Cough for 11 months baby. Some advice!

Hello doctors, I need some advice regarding this. My son is 11 months old and his last checked weight is 8.5kg. last Christmas 26 dec 2023 his cold started, and severe cough, I was at my in laws house, a very close relative who's  also a post graduate doctor suggested to give b cure syrup, that's dextromethorphan hydrobromide phenylephrine hydrochloride and chlorpheniramine maleate syrup. I was asked to give 2.5 ml.. it's been more than 15 days. his cough is still continuing, I decided to stop giving the syrup, now at this he vomits his formula milk twice due to cough. My son has a regular pediatrician, I'm just scared to text her now about his condition, I gave medicine without talking to her. What should I do. He had a running nose, but not now. It's just the cough that's bothering him. Please. Advice what should I do. I'm a first time mother, I have no idea how to handle. Please doctors suggest the next step.