Conservative paediatrician

My 7mo currently coughing with a lot of phlegm, brought him to paediatrician and he prescribed prospan, Zyrtec and zenmolin for 3 days. After I give baby, i found out that medication can be very harmful to babies because their livers not fully developed... super guilty. Will there be any long term effects? Any recommendations for more conservative paediatrician who don't always just give meds?