The reason the medicine not working because they are mostly for dry cough.

They are cough surpressent. They work immediately after 15 min you take it. But cough will come back once medicine effect gone.

If your cough is viral infection with mucus one those medicine basically will be going out from your buttock without any effect.

In that case, just wear medical mask, wash hands using soap, sanitize your phones regularly, don't go out often, take immunity boost milk, vitamin C, and sleep. This is to prevent any secondary infection so that your immune can focus on fighting off your current infection

Cough 1 week small matter.

I cough min 1 - 3 months since covid-ed

I will just get cheap anti histamine behind the counter because it's a control item

Take that for the stupid cough to stop and allow the body to supress the spreading mechanism forced by the virus via coughing.

That stop, virus will die out.

No cough medicine needed.

Virology paper i took during undergrade really paid off.