How do I know what to eat, how much and the right amount of exercise?

I have been struggling with my weight for years now. I always start exercising and do it for one and am unable to move the next day. I eat late at night often. I want to become a vegetarian so that I can lose weight sooner. I normally eat big meals and never any breakfast cuz a coffee with cream and 3 sugars. How can I keep myself motivated? I weigh 210lbs and am 5'10 in height. I do not exercise at all basically and when I do it I am usually too sore the next day. Way I try to exercise are walking swimming and rollerblading. I need to build endurance so I can exercise regularly without getting so sore. I am trying to quit smoking as well. I want to be fit without joining a gym. So far I k ow 3500 calories =1 lb ... I can't even do any workouts without being out of breath... 10 PTs for best answer and my main problem is my stomach is like a michelin tire ... I feel terrible