Guppies can live waayyy longer than to years, taken care of properly. I would think you are having a ammonia spike. Take your water to your lfs ASAP and have it tested. I have noticed that oyu post about alot of tank problems. I would suggest instead of buying MROE fish, or stuff you dont need, save up and get a test kit. If you test once or week, or whenever, you can prevent the problem with a water chagne before you get the outcome.