First off, it's a great question. Let me dissect a few things first:
healthy eating guy
Very few people really have this one dialed in. Maybe you do, but odds are you don't. There's a great website I've used called Body Recomposition and the writer is a pretty qualified guy who goes into nutrition.
Speed and endurance are the two primary levers you can play with as a runner. And when training, you are generally tackling one or the other. You combine them both on race day, but that tends to beat your body up pretty hard.
In the 5k distance range, you have three types of training that come into play:
- Endurance (Long Slow Distance): the idea here is simply to subject your body to a bit longer than your longest event, as it relates to time, not distance.
- Race-pace: you're going to run at your actual race pace for your actual distance. This tends to be very hard on your body and is reserved generally only for race days.
- Interval training. This can come in multiple formats, but hill sprints and fartleks are common.
Running really can be pretty grueling, and "getting your legs" (have the endurance and speed you need to feel comfortable at your level) takes some time, there's really no shortcuts on that one.
I'd recommend you try two strategies:
- Use a wrist watch, and every week try to have one day where you dedicate it to increasing your non-stopping time, maybe just by a single minute. In 6 months that's roughly an extra half hour of running, so although it's incremental it's certainly do-able.
- Pick another day, and try some intervals. Crank up the speed for a minute, then drop down to the slowest jog you possibly can, then crank it back up again, rinse, repeat.
Although "speed work" doesn't seem like it will help your endurance goals, it's actually anaerobic threshold training by another name. The ability to cross back and forth between aerobic and anaerobic activity isn't classically thought of as endurance but it's critical to increasing your anaerobic threshold and real-world stamina.