As a former distance runner myself, I can tell you there is plenty to do outside the weight room to increase your fitness. One of my favorite partners to running is swimming. There are so many ways you can get fit swimming. You can swim laps and you can also swim in a recreational pool with your family and going up stairs to a slide and sliding down the water slide and climbing up the stairs right away over and over again will keep you quite fit. Sliding down the slide also can release endorphins and dopamine just like you get when you are on a final sprint to the finish line in a race and that, as you know increases fitness levels as well.
I also recommend stopping along your running route at a park or side of the road to do lunges and pushups. You can also do squats and plyometrics and pull ups on the monkey bars. V- ups on the corner of a bench can keep your abs strong for your running efficiency as well.