Are my lungs already damaged?

You don't have lung cancer, but you might have either allergic bronchitis or reactive airway disease (similar to asthma without the chronic inflammation). You didn't mention a cough. If you do not have a cough then it is not likely to be bronchitis or RAD. If you do have a cough, there is almost certainly some degree of bronchitis. If you have no other symptoms it is at least partially if not fully anxiety-related.

I agree with the doc too: NO ONE should ever have to suffer through smoking indoors. It causes a host of problems over the long term and he has no right to subject you to it. It is your living space as well and -- since he can't divide the air -- you have a right to clean air without restriction. He has the option to smoke elsewhere; you do not have the option to breathe elsewhere.

Best wishes

Sound more like Asthma or an allergic reaction, lung cancer takes much longer to develop, 20 plus years.

I have the same problem with the people down stairs I bought an air purifier 4 about 140.00 bucks works fine

I suspect at this early stage your symptoms are more due to anxiety than any physical damage. However I do not in any way condone smokers inflicting their poisonous pollution on innocent bystanders. He should only be allowed to smoke outside!