Deductions & credits

I got a letter stating that my return is being held. I called and they didn't have an answer for me? The letter did however state I didn't take any action but I am concerned because this never happened before. It said they are reviewing my income and once finished either I would get a notice or my return. So do I have any reason to worry? I did get the earned income tax credit and the child tax credit for claiming a child. It's never taken this long before.