Reoccuring Cold and Breathing Issue

Hello,

I am 23 years old.
My weight is 63kg and height 167 cm

I catch cold and soar throat very frequently.
It looks like my immunity is very weak. When suffering from cold I get lot of phlegm. A lot of it.

I had minor asthma when I was young but it was never that severe that I have to use inhalers. Not with age the problem has decreased but as pollution issue is growing in our country I have started feeling breathing issue again.

Recently the breathing problem got worse and stayed form more than 2 weeks. I tried netural remedies like taking steam, salt water gargle and honey and ginger juice. Takin nebulizer with medicines – butecort and dualin also helped.
I have started wearing mask and my condition has improved but I want a remedy to this cold and breathing problem.

Please help !