Just something a friend of mine told me recently (he's a DR) he said panadol is the best cough medicine, as coughing is due to a rise in our core temp, and panadol brings it down. Worked for DD last night!! Gave her 3 hours relief out of 12 hours.... (better than nothing, and meant I had a nap from 11.30pm-2.30am)!!!
Also vicks vapour rub on soles of feet (socks on over the top) helps sometimes.
Also watch with the humidifier, I have found if used for more htan a few nights, can make the cough worse due to dampness and mould etc.
Good luck, I hear you, every time DD coughs my heart jumps and I feel for her so much. xoxo