How long baby recover from bad cough

How long did your baby take to recover from a bad phlegmy cough? As he’s still very young, they dont have medication for him. Gp check his throat no tonsil pr anything, just a little red and lungs is ok. He’s only 3.5 months old. Heard alot of mummies using euky bear but i read up that we can only use euky bear when baby is 12 months old, or atleast 6 months. Any other remedies ? Or just have to wait for them to get over it naturally? Which im not sure how long And if your baby is attending infant care do you still send them to ifc