Hi,
noise and fluctuations my have various sources:
(even three lines of text can´t give useful informations)
* noisy power supply
* wrong schematic
* wrong device selection (OPAMP, capacitors...)
* wrong filters
* bad PCB layout
* noisy sensor
* thermal drift of sensor
Now it´s on you to find the root of error or to cure it´s result.
Good informations are:
* schematic
* layout
* scope picture of error (magnitude, frequency /-spectrum...)
* timing chart
* desription of magnitude in volts or LSB, plus information like Vp, Vpp, Vavg, VRMS..
Klaus