5:30 and 19:20 are good times, and you run pretty high mileage, so your weight really surprises me. Fat loss is probably a lot more difficult for you than the average person if you can run that much and still be somewhat overweight.
I would strongly recommend being careful with weight loss and talking to a doctor and nutritionist. Rule out any hormonal issues (if you haven't yet). Don't try to cut calories a lot while running your peak mileage or hardest workouts; any weight loss of more than 5 pounds needs to be done in a time of minimal training stress (sounds counterintuitive but will be the best way to prevent injury. Cutting calories while running high mileage is a recipe for stress fractures and burnout, even if you don't fit the stereotypical idea of the super-skinny injured runner girl). Try supplementing your running with biking, swimming, weights, and be super careful with diet and see where that gets you. If you're still a little overweight, maybe your body is just unusual and needs the fat.
That said, if you are able to safely lose the weight and keep it off, you could probably run at least 40 seconds if not a minute faster in the 5k, and about 10 seconds faster in the mile (the longer and more aerobic the activity, the more weight makes a difference. Miles are pretty anaerobic. So don't expect to be a 4:40 miler off weight-loss alone).