flooring had too high a moisture content when it was installed. I suspect that trouble emerged when you began heating the house, driving relative humidity down. There also might have been too much clearance between the tongue and groove sections where adjoining floor boards interlock. This is a milling flaw and would account for the fact that you can push some boards down. From the pictures you sent, I can see that the boards have cupped slightly, causing the unnailed, groove-side of each floor board to rise. This creates the ridges you see and feel.

As with most wood flooring trouble, there is no easy fix. I expect that the ridges will go down again as humidity levels rise after the heating season is done. If you still find the condition of your floor unacceptable, the only thing I can suggest is having the floor sanded and refinished at a time of the year when the ridges are present. I wish there were something easier I could suggest.