Cloudy Fish Tank!!!?

So i have had my fish tank for about three weeks now and it has about 5 fish in it. I havent had big problems untill two days ago. I used Kordon Amquel plus because there was some ammonia in the tank and nitrite. I also used Doc Wellfish's aquarium water conditioning kit. The water started to get a bit cloudy but i wasnt to worried about it untill this morning when i woke up. The water is verry verry cloudy and i tried to do a 25% water change but it didnt work. The fish seem to be breathing verry hard so if any one can help me and let me know what i should do???? I was wondering if i should do another water change?