What's going on with your lungs, exactly? Is there mucous? What does the cough feel like? Does it feel like there's an ongoing infection? Different herbs for the lungs have different effects, depending on what's going on in there...
I would suggest some yogic breathing,
Pranayama, to strengthen the lungs and cleanse them. You're right, oxygen is a good idea. When I have lung stuff going on, I'll often do some steam inhalation as well - take a pot of clean, just boiled
water and put your head over it with a towel draped over you to keep the steam in. You can add a few drops of essential oils, particularly if you think infection is involved - I use eucalyptus, tea tree, and oregano often - they can be strong, so go easy and close your eyes!
Also consider the
root causes of your problem, and whether you can mitigate them in any way. Can you wear a mask for jobs that involve a lot of dust or possible mold? Herbs can help strengthen and tone, but they can't make us immune to the bad things we do to our bodies...