As others say, you are not fit. I had the same symptoms in my first week of Army Basic Training. I did puke. I was a better runner after 8 weeks of Basic. In Advanced Training (also 8 weeks), I had a Drill Sergeant who loved to run LSD (long slow distance). He would take us out, make a U-turn, and return to the barracks. About half the recruits would walk back to the barracks. It was painful, but I thought the DI knew what he was doing and I certainly needed the pain experience. I always ran the entire distance. Next came Jump School. This is two weeks of running, with the 12th day being LSD and you either made that run or flunked out. I can't describe how tough that run was for someone who was puking about 5 months earlier. What helped me were two SEALs who got on both sides of me, without any touching, and just kept encouraging. My point is that you can go from couch potato to Airborne in less than 6 months if you try.