So you like speed and to challenge yourself? Then we might suggest you take a look at the sprint interval training. Another format of the interval method but different..
The endurance training is meant to keep you running at a stable speed without taking any sort of brakes from this. If you are still at a beginner level..
The endurance run is a nice tool to see how long you can go at your steady pace. But after a while of doing this, it might not be enough of a challenge anymore.
If the last session was brutally intensive and you feel the burn this is because your muscles have been stretched and they need oxygen to restore.
A good way to increase your stamina fast is with the use of interval training sessions. This consists of short segments with a lot of speed changes.
It might seem like you always want to have the flattest terrain, but just like treadmills, it's fun to look for some terrain with height differences as well.