Bad Touch

So it all started out last September when my co-workers gave me two little goldfish who I kept in a small plastic pickle jar. I figured why spend the money on the foo-foo stuff for the fish if they were just going to die within the month. However, much to my surprise, they kept living! So I thought it was about time to buy them a bigger tank, with the filter, rocks, tank decorations, and a couple more friends to hang out with.

Well... it all started when the next morning I woke up and one of my new fish was dead! I was sad and just figured it was probably from the trauma of moving and the rest will be ok. Then a couple days ago I noticed the huge fish I just bought was being really lazy and was just laying at the bottom of the tank. His head was growing white and he had a big protrusion from his side.... which looked really weird. Well.. the next day he was floating... DEAD! I was just glad that it was not one of my original fish because I grew quite attached to them. However, this morning I woke up and one of them were DEAD!!!!!! I was quite angry... so I immediately transfered the two living ones to a new bowl and new water ( which was distilled and room temp so it was safe for them). I clean out the tank really well and put new water in it and waited until I got back from work to transfer them to the new clean tank (not that it was very dirty before I washed it!) Now the other one of my first fish is looking pretty grim... barely floating and a little lifeless. I have NO idea why they are dying.... do you think that one of the new fish could have had a disease?? I made sure to feel them enough but not too much.. their water has a filter and nothing else should be wrong with them! Does anyone know why my little fish are dying??
It makes me really sad :(