Lost water pressure after demo of bathroom, prior to any plumbing work. After tile on floor was torn up, pipes were under tile.

Do you have this loss throughout the house or just in one section? Have you unscrewed the aerators and cleaned the screens because it sure sounds like you've disturbed minerals built up in the pipe walls and it's now clogging your aerators and the inlet ports of your faucet cartridges. Answer my question and I might have a solution for you, Back to you, Tom