If you can put a low value resistor into the ground return path, you can measure the "ON" state current.
Remember to calculate the mark / space period and apply this as an averaging factor to calculate the average current.

The voltage accross a current sense resistor will be quite low, and will probably need amplifying using an opamp to bring it into range of the PIC.
Alternatively, use a chip designed for the job! I had a recent application where I needed to measure the current at 50 volts. The INA206 is a current sense amplifier upto 75 volts above the PICs 5v. Easy to use as well.

Tim.