Looking for the "magic"

I just got back from my morning walk with my neighbors dog. It's a beautiful day out and I love walking. I even ran (a little) down a couple of hills with her.
I've been busy this last week getting my house ready for my party that I had on Friday night so I haven't gotten to "my plan" of going to the gym and the park but I have been taking Morgan (neighbor's dog) on short walks around the neighborhood.  I'm watching her until Monday night so at least that gives me the motivation to get out a little.
I have a long way to go to get ready for the 5k in 3 weeks if I'm going to run..I'll be all right to walk it...I do that (3 miles) at the park with no problem..but I really want to get my time down to at least 30 minutes and to do that I will have to run part of the way.
My lower back has been bothering me a lot lately and I know it's because of the extra weight I'm carrying..also my knees are feeling it and the only way it's going to get better is if I take off weight. I really hate the "aches & pains" that goes along with being over weight and I really NEED to get myself back to where I feel good again. I'm not going to say I need to "lose" it because then there's a chance I might "find" it again..Of course this is what I said the last time I took off the weight and I still put it back on. This time I really need to find the "magic" way of keeping off what I take off. Funny thing about "aches & pains" when I feel them from working out it's like a badge of honor..I know I'm doing good.
I know with hard work and motivation I can take off the weight and get back in better shape but truthfully I'm worried that I will do all this and then to only gain it back again. That's what has happened to me 2 times already in the past 10 years. I feel that at 60 years old I'm running out time to keep playing this "losing game"
so now I'm on the search for that "Magic" way that has worked for others who took off the weight and kept it off...I'm pretty sure it's through "HARD" work..there is never an easy way..dang!.