What's the problem with my power steering?

There is a slight whining sound coming from the pump and the sounds gets louder the further the wheels are turned to either side. Also, when driving the car, the steering feels slightly stiff and awkward, plus the steering wheel doesn’t return to center after making a turn. The belt is tight, and there are no leaks, the fluid level has not lowered any since I last checked and marked it during my last oil change in December, there are no puddles under the car either… Just wondering if anyone can assure me that it’s the pump that needs to be replaced, or if the problem could be in the rack… any thoughts or suggestions are appreciated, Thanks.