I was wondering if you lose stamina when you workout and gain size. And Can you tell me if there is a way to increase your stamina while getting bigger and heavier.
The best to increase or at least keep your stamina for long distance running would be to make sure you are doing at least one long slow distance run, one medium distance run and 2-3 regular "easy" run in-between them. Don't get me wrong, weight is your enemy and there is a reason why runners are light and small, but there are runner who are 200+ lbs. that will finish a Marathon.
Your weekly schedule would look something like this: Mon -Rest Tues Easy -(4-5 miles) Wed Medium distance run (7ish or speed) Thurs - Easy Fri - Rest Sat LSD - 10-20 miles Sun Recovery
Of course there are a number of different goals for distance, time and injury prevention. I ran a Marathon this summer and noticed guys running with my who were much larger than me who also finished ahead of me. The key will be to consistently run every week and put that base milage in. The big factor for heavier people is how to do that without getting injured.