Did my Mom's smoking affect my endurance as an adult?

I’m a 24 year old female, not overweight and in generally good health. My mother died of advanced lung cancer this year brought on by her excessive smoking habit of two or more packs a day for 30 years.

For as long as I can remember, my Mom was addicted to smoking. Unfortunately she also smoked during all of her pregnancies. My brothers and I were all born full-term and healthy but I noticed that I sometimes I have trouble breathing.

I’ve never been diagnosed with asthma but running has always been especially painful. I was almost always the slowest kid in my class and even the obese kids could outpace me at times. Even running a mile would cause me to fight for breath and sometimes cough up blood. And trust me, I wasn’t smoking at ages 5–10.

Now that I’m an adult, I have maybe one cigarette a month when I’m out with friends but this problem has affected me all my life. I’ve gotten more into fitness lately as a way to get healthier and deal with my grief but running remains a challenge. I find that a half hour of brisk walking interspersed with jogging is about all I’m good for at this stage and I feel pathetic for it.

On the outside, my body is somewhat conventionally attractive by society’s standards so this isn’t just a weight or looks thing. I want to be healthy and athletic for once in my life but I’m afraid I never will be because I run out of breath so fast. It’s like my legs and muscles can keep pushing buy my lungs hold me back.

Is it possible that my Mom’s smoking during her pregnancies affected my lung development? Neither of my brother’s are good runners either but the one is 6’8 and very muscular and the other is very overweight so that could be why.

How can I improve my endurance over time?