The reason I thought high pass filter was because the OPAMP (as i understand it) works best when the frequency is higher rather than lower.
You understand it incorrectly.
If you filter before the amplifier when the signal to noise ratio is very low then yes you can end up with more noise.
However, improving the layout and decoupling around your circuit can greatly reduce the noise. Also using the correct component values, not just ratios will help.
So you need to post a schematic of what you have built for further help.
but I don't know what are OP:s
Operational amplifiers