Good day. Has anyone encountered a buildup of phlegm in the throat of …

Good day. Has anyone encountered a buildup of phlegm in the throat of babies (ours is 4 months old), dripping down the back wall? What did you do in this case? Doctors say it will pass, the formation of mucous membranes, but for three weeks now such a phenomenon and the baby is disturbed by sleep, eating and just being in good mood.