what do I do when the drop rate for home plumbing isn't enough?

Had bathroom renovated, whirlpool added, separate shower etc...It's been a nightmare ever since. Toilet backs up in shower, tub won't drain, every faucet in the house gurgles. Home Depot did the reno and won't return calls. The septic system has been checked. Any ideas what might have been done to render 20 yrs. of problem free plumbing to this mess?