When did you start exercising Chirpy? It's really not necessary to run really fast to get fit. As Jenna said, you need to build up gradually. If you get too hot, you are risking heat exhaution, which can be fatal. It sounds like you are over doing things.
Just make sure your heartrate increases to between 65 and 85% of your maximum and keep it at that level for at least 20 minutes. To work out your HR training zone, you take the number 220 minus your age x 65 or 80%.
So if you are 20, it would be 220-20 = 200 x 65% = 130 beats per minute (BPM). Do the same to work out 80%. Try also to vary your training programme, don't use the same machine over and over, use others too. Doing the same programme, will cause your body to adapt to that particular type of exercise and your fitness goals will not improve much.
Try to do some weights too, I expect you will need good upper and lower body strength for activities you have to do in the army.