Currect measure through ADC and shunt
Use a high-side current sense amplifier.

These ICs are specifically designed to do this job: Amplify a tiny voltage across a tiny resistor placed on the "high side" of your circuit.

There are thousands of them, the first I found is the LT6106 from Linear, but there are many more. Here is a link from digikey to start with.

They have an integrated amplifier, and often use a clever and very simple feedback "trick" so that you just have to add two resistors to set the gain you want:


(From the LT6106 datasheet)