Build a Foundation
Add some variety to your exercise routine. Run one day and strength train the next. This will not only hold your interest in the workouts longer, but it will give your body the time it needs for recovery. Additionally, you are covering more muscle groups throughout the body and keeping the workouts motivating and different.
To build up endurance for your 5K race include some interval training as part of your regimen. Use hill sessions and up-tempo to your runs to do this. Hold a steady running pace where you do not feel like you are just about to die, but that you can keep going.
Head to the track for shorter interval runs while learning to pace yourself. Learn to conserve your energy during the first part of the race and then to let go in the second half so you can make it to the finish line of you 5K race.