A diet plan would be to eat 5-6 smaller meals (about 3 hours apart) to help keep your metabolism up and not to store excess carbs as fat. Basically up your protein, lower your refined carbs (eat complex carbs/veggies), eat healthy fats (some nuts, olive oil/flaxseed oil/peanut butter). Drink plenty of water and cut the sugar. You may be doing this already as part of your running program. The idea is to turning your body into a fat burning machine using the calories as energy to fuel it.
You can include a weight/resistance program to this along as this does force your muscles to work harder and keeps up your metabolism longer. It will also strengthen your legs and develop upper body strength too. You can perform the lifting on the days you are not running. A three day split for about an hour.
I was like that as teen. I was never thin for my height (5'6") and was considered overweight at 155 as a high school freshman. Being largeboned and broadshouldered did not help...I just could not get my weight down. BUT I did ride a 10 speed all over San Diego as my main form of exercise for years. So I was fit, cardio wise. This at a time when "Twiggy" and Cher were the models of what teens wanted to look like. When I got to college, my weight had gone up alittle but I was still riding my bike 7 miles too and from college five days a week. Tried all sorts of diets then to help lose my weight. Rarely ate most of the time. Forget about running....just did not have the speed and preferred riding the bicycle.
When I married, I moved to SW Arizona with my husband on a placer gold claim. Did a lot of walking around in the hills there when not helping him in his blacksmith shop. There was no where to ride a bike there and so...gained weight. My husband was a "meat and potatoes" man and so you can figure where MY figure went.
After ten years, we moved and I had two kids by C section. Was 245 by then and ballooned up to 260. Still kept somewhat active raising animals but not enough. Hit menopause in my mid 40s and drifted down to 245 by age 50. Because of my rural lifestyle, I was naturally strong....despite my weight. But age was getting to me and so was the weight.
In the Fall of 2002, I took a college Women's strength class and for three days a week/90 minutes worked with resistance/lifting to improve my health and lose the fat. Stayed with it for a year and lost 60 pounds. That and learned eating 5-6 smaller meals was not going to make me fat (fell into the "female diet" myths for years) and learned to moderate/improve my diet. Between that and the lifting...at 52, I am back down to wearing pre marriage jean sizes although, by the scales, I am abit heavier than what I was then....33 years ago. This is from muscle, though, rather from fat.
I still keep to my diet and workout at least two times a week at home to maintain what I have lost and gained. I still cannot see myself as being thinner though....just a body image in my mind. According to old insurance height/weight charts, I should be 130...145 at the most. But in my eyes, I would look like a bonerack. 160 yes ( and this this acceptable nowadays), but anything less....just cannot wrap my mind around a thinner image. In the old days, I would have been considered having a "good, old fashioned Scots/Irish farmstock" body. Hefty but not that fat. My younger sister has kept herself in shape by doing semi professional Ethnic Middle Eastern dancing for years. But has the same problem as I do even at 5'4" and 46....she is not thin by any means. Just quite fit and firm.
So where I am now at 52 and at 180, I can live with that. Maybe someday, I could get down another 20 pounds but I am not going to anquish over it. My health has improved immensely. I have strength and flexibility back. And I can now run after a 6 year grandchild without huffing.