I assume you're still using the test strips to test your water, those results you got could very well be inaccurate. As mentioned before, invest in liquid test kits, they are far more accurate and last in the long run. A little more time consuming, but it's very easy and helps a lot.
It's good to hear that your tank is cycling, guppies are hardy fish, and will most likely survive in the cycling process, however, survival is not the only thing you want, you want your fish to thrive. They may become ill or possibly die, but from what you described, it just sounds like the ammonia and nitrite are taking a toll on them. As Jermey had said, the nitrites bond to their blood cells, making it difficult to intake oxygen,that is why you see your fish gasp for air.
You could always buy a bottle of bacteria to boost the cycle. Most pet shops and fish shops carry bottled bacteria to add to your tank. It's just a way to introduce more bacteria, but I on't think you'll need this. I would say just let your cycle continue, invest in liquid test solutions so you can keep track of the nitrification process.