I'm pretty new to running and can only
run for 2-3 minutes at a time.
I was in your situation. During a martial arts belt test, they sent us out for a couple-mile run, and I wound up having to walk most of it. Since I knew it would only get worse at higher belts, I decided I needed to become a passable runner.
So here's generally how I did it, using a battery-powered kitchen timer, and running three days a week with a recovery day in between. I focused solely on time, not distance, and would do each step either for a week (three running sessions), or move on faster if I felt comfortable but not like I was pushing myself into injury.
- 15 minutes, alternating run one minute, walk two (1/2).
- 15 minutes, alternating run one minute, walk one (1/1).
- 15 minutes, 2/1.
- Stick to 15 minutes, but progressively lengthen the cycles (3/1, 4/1, etc.) until you're at run seven, walk 1, run seven.
- Run 15 minutes straight. By this point, it will probably be a breeze.
- Increase the time by 2-3 minutes until you get to 30.
At that point, I was doing about 4 km in 30 minutes, which is really a jog. After than, I stuck to 30 minutes but worked on lengthening my stride, which increased my speed and distance.
Worked great for a chubby old geek in his late 40s whose prior running experience was mostly in high school gym class. :-)
Now I consider myself a runner, and have done it literally around the world while on business trips.