Try this. It sounds like you've been doing the jogging thing for a while. It's time to change your mode of cardio. Switch to your next favorite cardio machine, or just walk on a treadmill, instead of running. If you're running on a track, or street, do a fast walk, maybe with little bitty dumbbells in your hand.
Here's why... Have you ever looked on a cardio machine, and seen that little chart on the side, that shows heart beat ranges for "fat burn" and "cardio", for different ages? Well, that chart is not accurate for YOU, but it's probably pretty close. Anyway, in one to three days, take your Resting Heart Rate three times a day. VERY FIRST THING in the morning, as you sit up, but before you stand up. Sometime in the middle of the day, after you've been sitting for 10-15 minutes, peacefully. And one other time, in the evening, more than three hours after working out. Take an average of those #s, yes you'll have to write them down to keep track. Once you have the average Resting Heart Rate (RHR), you're ready for this formula:
220 - Age = Max Heart Rate (MHR)
[(MHR - RHR) * Training Percentage] + RHR = Training Heart Rate
For example on a 27 year old with a resting heart rate of 64:
220 - 27 = 193
193 - 64 = 129
129 * 50% = 64.5
64.5 + 64 = 128.5
Now, do that again with 60%, and 75%. You now have your training zones, like the ones on those charts. Between 50% and 60% is your FAT BURNING ZONE, and between 60% and 75% is your CARDIO ZONE. Anything over that, you're burning muscle!! Don't go in that range!! Unless you want to look like a Marathon runner.
I'm willing to bet, when your running for 45 mintues, your heart rate is getting pretty close, if not in, that muscle burning zone... so that's why I suggest walking... ON AN INCLINE!!
Look at it this way. I, personally, can walk on an incline of 15 (highest ours go at my work/gym), and start walking at a speed of 4.0. Then eventually get down to walking at 2.2 to 2.5, for long periods of time. That right there keeps my heart rate around 155-ish, which is my 60%. Don't hold on to the railing, or anything, just let your arms swing. Gets your heart rate up.
So, first of all, a change in cardio mode will send your body into shock again, like it did when your first started running and lost some fat. Second, the walking, or whatever, with your heart rate in the right zone now, will really start to burn off fat.
Next, like mentioned above, watch what you eat, and try to get the calorie intake below what you burn off in a day.
BTW, if you want to know what good Resting Heart Rate #s are:
80+ is pretty bad, you need to work on it.
70+ is pretty average, from what I see at work
60+ is getting better, bottom range of average
50+ is you're doing really well, and in pretty good shape
40+ is really bad ass, and your heart is VERY healthy... or unhealthy if you're sick or something
Lower than 40, you MUST be a Marathon runner, or something like that!
Just imagine your heart only beating 38 times in a minute. More than a second between beets.
Sorry this was long, just trying to share my knowledge!
Let me know if you have any questions. This is my job.