I think you need WAYmore gain and a proper instrumentation amp (very very good CMRR). The change in resistance of a strain-gauge is measured in tiny fractions of a percent, so gains of 1000 or more aren't unreasonable.
This might be useful:
http://cerulean.dk/words/?page_id=42 there a gain-resistor of 10 ohms is used, meaning a gain of 6000. Sounds more likely than 50!