Is there something wrong with my lathe ?

As the title suggests something feels a little off with my lathe. I have an MC900 bought 2nd (maybe 3rd) hand and I have fairly recently replaced the drive belt on it. Even more recently it feels as if it isnt spinning in a circle, more like an oval, my work, be it a pen or a bowl, feels like it is jumping in and out. I am not sure if this is something that is wrong with my lathe or if it might be just because have made a few things now and I am becoming more sensitive to it ? My 1st thought is possibly the drive wheels are a little out of shape, 2nd thought was possibly bearings, 3rd thought was perhaps the tail stock isnt quite square ?

I havent had this lathe very long and I dont really want to have to dump it and buy a new one if it might be something easily fixed (it wouldnt make the boss happy either). Anyone have any experience with this problem or perhaps a suggestion how I might get it "straightened out" ?