Sounds like bronchitis. All my colds turned into this - headed right for the chest where they lingered for 3-4 weeks at a clip. It's worse at night partly because she's tired, and also when she lies down. It also means that she probably doesn't sleep well due to coughing, and that lack of sleep has an impact on future health.
Vapor Rub is of limited effect other than some possible comfort. It's pretty unproven even though people like to do it because it feels like there's at least something to do against this stubborn cough. Honey can help soothe a sore throat, but if her cough is from deeper down, it's not going to do anything for the bronchial inflammation.
I did cellular nutrition and my problems went away. I don't get colds anymore, and so there's nothing to go down into the bronchial tubes. In the past 2 years, I have added in the new anti-inflammatory that's plant based. It helps with immune system boosting as well.
If this is viral, there's nothing the doctor can do other than treat the symptoms with cough suppressants. I know you are frustrated. I have friends who had their little kids on nebulizers and inhalers too, until they got to the point where they were able to prevent all of this. It's about immune system support, I'm afraid. It's much harder to treat after the illness than it is to prevent the illness to begin with.