How do I keep motivated with food and exercise??

For the last 3 or 4 years I have always said I'd lose weight and I'd get fit and I'll exercise and eat right even joining and gym and going to a weight loss class and after 4-6 weeks I get bored and go back to my old routine of sleeping all day and eating all night and I'm sick of it. I kept trying to make excuses like I'd do it when I'm ready and that I wasn't to bothered losing the weight, until about a month ago and my friends put up pictures of me at a Christmas night out and It hit me, I'd let myself go way to much and I just looked horrible and I felt even worse seeing those pictures.

I was never big, it was only after I left school in 2009 and had nothing to do, I wasn't doing regular exercise and I wasn't eating at regular times and in the last 3/ 4 years I've gained 5 stone / 70lbs, and 14 of those pounds have been since September.

Last week I decided that's enough, I'm in my 20's and I have to do something now before its too late and so I cut out all the junk, chocolate, fizzy drinks etc... and switched all my whites to wholemeal (Bread, Pasta and Rice) and I have been eating 3 meals a day and 2 snacks but still can't find the motivation to exercise.

How has everyone else kept motivated and what kind of things have you ate or not ate that has helped with your weight loss? I need help and don't know where else to look for it. Any tips or advice would be great