Why is my fish aquarium water cloudy?

I have a 55gal with about 10 fish, small-med size rainbows, platies, swordtails, and a clown loach. For the past 2 weeks the water has been very cloudy, and the amonia level has been shown as high. I change my filter every month, and change about 25% water every 2-3 weeks. I cant pinpoint what is going on. In between these two weeks, I changed like 80% of the water to see if it would get better, but it didnt, and got cloudy again. Is this a bacteria outbreak? No fish has died during these two weeks of cloudyness... they seem fine and fairly active, but arent swimming quickly (prob due to the haziness of the water). What should I do?? Please help!