The back taxes shouldn't have a lot to do with it because they would simply deduct those from the refund you currently have coming.
'Further review' simply means that. They're looking into it a little closer. That usually happens because some of your deductions may look a little suspicious or maybe you're claiming too many expenses in relationship to your income. It certainly may take them that long, but it will probably be ok. I would say "Don't worry about it" but you can't do that, can you, lol?