first of all, make sure you are taking in enough water n you have to have plenty of fresh air.also you must make sure you have enough sleep but not too much. because sleeping for too long might bring you to headache.
you better not to drink coffee or tea(tea with milk) coz these kind of drinks make you more likely to vomit.
is it a chesty cough?
and does the decongestion affecting your face area as well? do you feel blocked round your face?
are you coughing up phlem? what's the colour? if it's yellow or green, you really should see your doctor coz general medicine in the pharmacy are not strong enough to help you as you might need some antibioctics.
if is it worse at night, that means there is something dripping down at the back of your throat.
if you got a temperature, try some PARACETAMOL, you can find it in watson's , those got a pharmacy in there. it can also help the pain.
you might need some SUDAFED DECONGESTANT tablets or the SUDAFED COLD & FLU(this one already got some paracetamol so you do not have to buy the paracetamol separate), these 2 product are avalible in UK but not sure if you can find that in HK, but i can tell you what's in there
SUDAFED DECONGESTANT
active ingredients::
pseudoephedrine hydrochloride 60 mg