You don't say here, but what kind of cough? Dry and unproductive or wet and productive? Cold or allergy?
If asthma/allergy I highly recommend seeing a specialist -- my daughter wasn't really helped when we allowed her pediatrician to prescribe and educate us RE asthma medications for her RAD and seasonal rhinitus (many ER visits later...):( We do many things differently for her when she coughs than for my son with his cold coughs...
If wet and productive, you can give decongestants or benedryl-style medications to dry the post-nasal, cold-cough combinations, prop-up when asleep so chest is raised. If dry and unproductive, you can give expectorants and use humidifiers or heat from shower or warm towels on chest and sinuses (dryer or wet) until productive, then above. Stand-bys for me are honey or lollypop to suck when awake, cold pops are good too, vicks always works for my son with some on chest and smidge under nose. If blowing nose a lot, then petroleum jelly on nose and lips for chapping. Wipe all your common-touch surfaces, like lightswitches and doorknobs, with Clorex in one swoop to stop reinfection:)
When medications are only 4yrs and up, I "cheat" and give based on weight or age percentage (give 1/2 dose or if in 80% weight give 2/3 dose) and I give as little as possible based on symptoms and reaction to medication. Then, I wait and see...
Good luck and if you want, you can email me too -- much experience with uncontrolled coughing:)