To add to all of Lisa's good advice:
Don't use those bags of shock either. Mostly, they are Di-Chlor, which ALSO releases CYA into your water.

A CYA of 100 is what I would consider extremely high, but manageable. I like 30-50, but you won't get there this season. Still, if you dump 1/3 of your water, you'll drop CYA to 100ppm. You will need to maintain a MINIMUM chlorine level of 8ppm (that's the FC reading) at CYA=100ppm.

If your pH is staying high, powdered pH lowering (dry acid, no matter what else they call it) may not work for you. If so, muriatic acid is available at any hardware store. Dilute between a cup and a quart in 5 gallons of water, wearing eye protection and gloves and add that to the pool.