Low side current sensing
Just need a basic non-invetering opamp cct to amplify the voltage between top of R7-9 and GND. This is an very basic circuit that you can find all over the interwebs. Tweak R1/R2 to change the gain. 

I set it so 5A gives you just under 3.3V as you requested, but you actually probably want some more margin in case it goes over. You probably also want some filtering the signal as BLDC circuits generate a lot of noise, which will throw off your measurements.

Hit simulate, DC sweep. Sweep I1 from 0 to the max current, and readback VOUT.







simulate this circuit &ndash; Schematic created using CircuitLab

EDIT: Added C1 for low pass filtering. You really ought to put the footprint in at the very least. Its going to be really noisy, and you will want to get rid HF stuff.