Fitness/Running Tips?

I play HS football and ever since last season ended i've gained around 25lbs and its not good. And since football season is around the corner im trying to get fit. Today was the first day i went out to run. I started with a 1/4 a mile walk then started doing some hills. The hill is a pretty decent size and my goal was 30 but i only got to 10 then i was really out of breath and light headed. Last year i could run 30 before i even started to feel anything. I just wanted to know if there is a plan i could do to not feel so tired or light headed. And also when i was running the hills before i even got tired my calf muscles started tighting up and hurting, and i don't know if this is relevant but i have big calf muscles. I also streched for a good 30 min. Just wanted to know what was wrong.