I am 5'2 and can sympathize... I started trying to lose weight when I got to the point of 128 pounds. I also want to get back to 115 pounds to feel happy again.
Here is what I do:
I've started eating healthier - adding snacks of fruit and veggies in between meals to get to at least 5 a day.
Stop eating after 5-6pm. (Generally - at least five hours before bedtime). And I mean stop everything. No soda, no juice, no fruit - just water. You wind up going to bed with a growling stomach, but it does wonders, since it forces your body to burn fat reserves over night for energy instead of allowing it to turn whatever food is left in your stomach into fat.
On your treadmill, I wouldn't necessarily jog - raise the incline and do a fast walk throughout. It will make you break a sweat quickly and won't hurt your joints. I'd try raising the incline in increments until you can do at least 5 minutes against the max. incline on your machine.
One thing that's helped me tremendously was the good old tae bo workout. It forces you to do a full-body routine and tones all your muscles. I'd recommend getting two of the original tae bo tapes and doing one day on the treadmill, the other with the tape exercise.
The main reason why you're probably gaining weight is this:
As you start exercising, your body thinks that it needs more energy and will start storing more of what you eat as fat.
Don't eat right after exercise - drink plenty of water, eat a big breakfast and don't eat in the evenings.
I've been doing this routine (minus the treadmill) for four weeks now and have visibly lost weight.
Hope this helps you too!