I have a Canon Rebel Xsi. It recently started being blurry in part of the picture (usually on the right hand side specifically). I'm shooting with an EF-s 55-250mm lens. I've always have very crisp beautiful pictures until recently. Is this a problem with the lens or the camera?

Also if there is an everyday AWESOME lens that won't break the bank, suggestions would be greatly appreciated!

When is the last time you have cleaned the camera?