Yes, listen to 'Mom. Your problem is that your water has something that's causing your chlorine to be eaten up. Probably something biological or ammonia.
I THINK a pound of Di-Chlor add about the same as 1.25 gallons of 6% bleach--ball-parking here, but I know it's a little more than a gallon of bleach. One gallon of 6% will add 12ppm of FC to your pool, so the pound of "shock" was probably good but it would have added something like 8-12ppm of CYA to your pool as well. 3 pounds of Di-Chlor shock would probably put your CYA in the 30-40ppm range (when starting from 0 CYA).
Still, go back to basics. Use bleach to raise your FC to 15 and check and adjust it 3x a day until it stops "vanishing".
Since 1 gallon of 6% will add 12ppm of FC, 1 quart will add 3 ppm. You don't need smaller increments than that.

Carl