For breathing problem in flight, how much O2 should I use?

Hello doctor,

I have had chronic asthma and allergies in my whole life. I am currently taking four puffs of Qvar three times a day, Accolate twice a day, Xopenex as needed and DuoNeb as needed (nebulizer). I am in control almost all the time. I also have a hyperactive immune system where I end up with chronic pneumonia. The last time when I traveled in flight, I had breathing problems for about an hour and then on and off for the next three days. I discussed this with my primary care doctor and he suggested that the cabin pressure exasperated my asthma. Then, the altitude change continued to stress my lungs. He suggested using an oxygen concentrator in flight next time. I fly again in two weeks and as needed. I did not know how much I should use. Is it reasonable to check my oxygen (O2) blood levels and then use O2 based on these readings? How many liters per minute should I start with? How long would I expect it to take to recover or increase the amount? Or should I just use the concentrator for the last hour or two of my flight and see how it goes? If so, then how many liters per minute should I use?