How can I increase senstivity of my emg sensor?
You are already getting about  80dB gain \$Av=50k\Omega/(2\pi f*47uF)\$ peaking just above 1kHz. 

You can get more 10dB lower frequency gain (if that is useful), by changing 47uF to  470uF now peaking around 4oo Hz like a HPF followed by a LPF due to gain BW limits.

If you increase C to 2.5mF you 10x gain at 200Hz up to 100dB which matches the spectral density of human EMG.



However big polar caps have high leakage with reverse voltages>10% of rated voltage then fail rapidly if current is high enough.

So a better solution may be to use another op Amp with special BPF.
Can you use bigger or better electrodes with pressure?