When my DS has a bad cough, we use a humidifier with a couple drops of eucalyptus and/or lavender essential oils, rub his feet with homemade "vapor rub" (sweet almond oil, lavender and eucalyptus EOs) and try to prop him up a bit so he doesn't sleep completely flat. This usually brings significant relief for him (and us!). I try to focus on things to help him relax (the lavender oil, massaging, etc.) and decongesting (eucalyptus, humidifier). Now that he's older, I've started giving him an herbal cough syrup made by Gaia's Children called Cough Syrup for Dry Coughs, but it has honey in it so your LO is still a bit young for it. It doesn't give him immediate relief, but it helps him get rid of his coughs quicker. I hope your LO finds relief quickly!