are soft erections permanent?

I am 29 years of age........I have been smoking on average 10 cigarettes/day for almost 10 years and i am not engaged in any physical activities like sports,walking, or any other thing at all for last 5-6 years and my eating habits would be include 50% junk and 50% healthy.........i m extremely concerned about my soft erection since it started when i got my first car as i stopped taking the bus for commute ( lack of walking )and having soft erection since last years i believe......... i still get soft erection in the nights n in the morning about 2-3 times but i m more concerned as the last thing that comes in my mind before going to sleep and first thing that comes in my mind after waking up if i have an strong erection......would changing my eating habits and exercising like walking or running everday and quitting smoking improve my situation or if it's permanent damage.......and if it improves how long would it take to get strong erection again.........PLZ HELP?