wrong measurment with PCB circuit

I fabricated a PCB board first time and used trace width of 20 mil for power traces and 10 mil for all others. When i check the circuit with dc input voltage (ex:50 mv- 600 mv) everything is perfect.
When i connect it to a real input (also a dc potential in the same range, ~30 uA current), the circuit receive signal much lower than original.Other parts of the circuit are working fine, just i am receving very low signal as soon as it is connected to circuit input.
Can it be due to the trace width. Or if you have any other idea or suggession please help.

NB: A little more about my circuit, the input pass through RC filter and then amplifier. The filter has nothing to do with the low signal, since i am getting the low signal even before filter. I had already been using same circuit with sholdering on veroboard, so the problem is not related to circuit design, i think .

Hi,
from my point of view it is not related to PCB trace width.(if your board may be single side board it may be get,because for single side you have set the trace width 40 mil )better check the circuit once again.

Thanks for quick reply....Its a single side board. I designed the PCB board and set the input trace width to 10 mil. So you mean it should have benn 40 mil??
Also is not it surprising the circuit works fine with a dc supply of same range without any problem.

Do you mean the DEC voltage is dropping from the power supply to the devices, a little diagram and more explicit on what the signal is would help.

Yes, the dc volage applied in power supply can perfewctly be measured and as i said the if the source of input is from from a dc supply no problem can be observed. I have attached the circuit fr convenience. its simply a filter plus amplifier.
The signal i am trying to measure come from a solution measured vs two electrode. Its quite similar to the battery.