Current monitor output doesn't respond to load changes
R3 is way too large. Its voltage drop will hit 3.3 V at a current of just 3.3 V/50 k&Omega; = 66 &micro;A, which corresponds to a load current of 100 &Omega;/0.1 &Omega; &times; 66 &micro;A = 66 mA.

If you want to measure currents up to 10 A, which would be 10 mA through R3, its value can be no more than 3.3 V/10 mA = 330 &Omega;. In fact, it will have to be much smaller than that, because you also need to account for the voltage drops across R1 and Q1.