Ai, batuk berkahak tu mmg berlengah-lengah kan, especially kalau ada phlegm yang stubborn. A few of us tried giving warm water or warm milk before bedtime to help loosen it, seems to help a bit dengan the coughing fits at night. Some mums swear by elevating the head with an extra pillow or folded towel so the mucus flows better, tapi tu lah depending on how your boy akan tolerate lah. Kesian dia struggling with drinking susu, but do check back with the doc if it's still lingering after 3 weeks, sometimes they might need something stronger or need to rule out if it's something else like asthma or reflux.