I can relate to you simply because I was a fatass at one point (227lbs; 6' and only 19 years old at the time) and now I consider myself pretty fit (180lbs; 21 and with a low bf %).
You have to start slow but stay consistent, and it's going to require a strong will. Keep reminding yourself that you want to change the way you look and feel.
How are your sleeping patterns and eating habits? Do you get at least 30 mins of rigorous physical activity a day?
A good starting point is to eat clean and eat smart. You don't have to do any diet bullshit. Just slow down when you're eating and manage your portions. Don't snack unless you have to and drink plenty of water. Eat fruits/veggies as snacks if you really have an urge.
Get plenty of sleep but don't oversleep. Too much/little will fuck with your metabolism.
Start walking/jogging at least 30 mins a day and begin some light resistance work. You'll feel like you're getting back into the swing of things and you'll experience that wholesome body feeling again. All you have to do is make sure you don't cheat yourself and stay consistent.
It's not rocket science and it worked for me.
E92 335i: Space Grey|Coral Red|Aluminum Trim
Hold out for the BRZ STI or... Rocket Bunny FRS. Update: Scratch that. I've got a 2015 5.0/6MT with my name on it.