Wa'alaikumsalam sis! At 4 months, memang susah sebab dia still too young untuk most remedies, better check with your doctor dulu to make sure it's not something yang perlu antibiotics ke apa. Dalam sementara tu, pastikan dia hydrated, elevate the head sedikit masa tidur, dan kalau fully breastfed ensure lah milk intake dia consistent sebab itu immune booster terbaik dia. A few of my mum friends swear by nasal saline drops to clear the congestion, memang helps with the breathing jadi dia sleep better, pero confirm with doctor first lah, especially since baby pa lagi. Hang in there, batuk bayi memang heartbreaking tapi usually it passes!