Arduino ADC confusion

I don't get it.
I want to meassure 1g-200g with an  #Arduino .
Alexis Wiasmitinow made me a PCB using the
http://www.robot-italy.com/it/3132-micro-load-cell-0-780g-czl616c.html
750g load cell and an op-amp with adjustable gain and offset.

When I place a 150g load on the cell it sometimes increases *or decreases*.
When I remove that load it sometimes doesn't return to the value it had before.
When I adjust the offset to get very small values with no load placed on the load cell, I get no change in the value at all. With higher offsets I get value changes depending on the gain.
But never more then 3-4 bit of resolution .

I'm using pin A1 on a Arduino with the LCD-Keypad shield connected (shield uses A0 and 4-10).
http://www.robotshop.com/dfrobot-lcd-keypad-shield-arduino-1.html

Any idea?

Update: We solved it via Skype chat (G+ hangouts only produced "server error" and "severe server error".)

I simply had my load cell mounted the wrong way. My load was in the wrong place!!!