Hello
Benadryl is an antihistamine, that means it's effective if you have allergic cough which is dry and with minimal to moderate mucus production. It is not indicated in productive cough which has expectoration.
So, does "heavy day by day" mean the sputum production is increasing day by day or just the dry cough severity is increasing, you should mention that.
Also ,get a COVID screening done.
Next Steps
1.A proper history with consultation
2.COVID screening