One end of the resistor is connected to my A0 pin and the other end is connected to ground.
Which ground? Try connecting it to an Arduino ground pin that is not otherwise connected. If you are connecting it to a common ground on a breadboard, that can make a lot of difference.
Ive never heard of the MCU pin can u please describe what it is ...
What I mean is the AGND pin of the atmega328p chip (or whatever other microcontroller chip your Arduino uses). It's a shame that the Arduino doesn't already have a separate AGND pin to connect to, however the boards I have seen use a ground plane, so dedicating one of the ground pins as an analogue ground is probably good enough.