Why does it feel different this time?

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Next month I will be 49 and since retiring from the Air Force 8 years ago, I have really left myself go. I have probably put on a good 50 pounds. I have half-heartedly tried to stop gaining or lose but without success or prolonged success. It's weird but this time it feels different. I'm not sure why. I'm pre-diabetic which I have known for awhile but ignored it. I've had to buy larger sizes but was ok with it. But somehow when my knees started hurting while walking up stairs I knew it was time to do something about it. I have been doing MFP for about two weeks which isn't long but I've been logging food every day and exercising a couple of times a week and have lost 6 pounds. My knees hurt like heck but I'm staying motivated. I tell myself to stay this way but I'm so afraid this "feeling" will go away. I love reading these posts and hopefully will maintain my desire to help myself. Could I really be at this point in my life where I can make a change?