1) Welcome - to WDWMagic in general and to the running section in specific.
2) Great work so far, especialy with the weight loss.
3) Baby steps. What you do not want to do is push too hard and injure yourself and then have a massive setback.
What sort of pace are you running ? You can drop it a touch slower and maybe bang out some more distance. Or, you can start to slowly add distance.
Most plans, when trying to build distance, have a number (2 - 3) shorter runs per week at a faster pace, and then a long run at a slower pace. You said you are doing a couple of 3 milers already.
You increase milage by a few miles per week.
For example
Week 1 - 3,3,4
Week 2 - 3,3,5
Week 3 - 3,3,6
Week 4 - 4,4,6
Week 5 - 4,4,7
as you get into longer long runs the shorts stay around 6 - 8 miles and the long becomes 13, then 14, then 15, then 16 ....
Of course if you are Nick (DonaldDuck) your shorts are 25
-dave