Best medicine for kids

Ok I need help because I feel like I’ve used every brand and they never work. It’s to the point where I’m using them all through the day every 4-6 hours as suggested on the bottle and I’m having to give it to my son for more than 2 weeks.

Any suggestions ? My son is 4. Nothing seems to work. I did give him robotissum for ages 6+ for cough but less than 2.5ml and that works at night to help him sleep, and constantly coughing throughout the night, but nothing else seems to be strong enough or helps. I hate having to give him medicine for over 2 weeks and the medicines aren’t helping.

Below are what I’ve used and didn’t work at all:

Zarbees (none of them do anything!!)

Hylands brand doesn’t work

Mucinex free form cold & stuffy nose

Equate brand for cough and cold

Chestal Kids Cough Syrup (made the coughing worst and bottle says to give every 2 hours)