| A professional runner 5'9" would weigh about 125#, so you are not ideal running size, but I doubt you'd want to be unless that was your livelihood.
Your story is typical, actually, you're doing better than most. Watch for an endurance sticky which should be out in about a week. That will give you tips on developing endurance, which is what you are seeking. In the meantime, run as long and as hard as you can, walk until your heart-rate recovers down to about 100, repeat, over and over. In time, you will be able to go farther and faster. | 
