Circles don't come out circular (Prusa i3)

Hello, everyone. I am having a problem with my Prusa i3.

It seems that sometimes when circles or rounded lines are supposed to be printed, they either come out square or extremely wavy in shape. This has been an issue for a while but I have just been able to brush it off for the most part.

I have attached two photos that you can compare to see what I am talking about. One photo is of the Repetier Host status (what the print should look like) and the other is the deformed printed lines (the wavy/somewhat square lines that should be circular)

I have no idea what this could actually be, so any help would be greatly appreciated!

Seems that I have solved my own issue! My Y-Axis belt has always been a little loose, however it never seemed to produce problems of any sort that I could notice. Well, since I had the printer disconnected earlier I decided to throw a tensioner spring on the belt and make it extra tight and that seems to have solved it completely! My print quality is great now, no more circle issues and just the general overall quality has improved extremely.

Hope this helps someone!

Must have been some really loose belts. I was going to say that is looks like an axis was sticking.

A lower first layer is needed too.