Another possible cause-
By any chance are you using calcium hypochlorite in your pool?
When I used it in the past with my DE filter, my pressure would quickly rise and I'd have to breakdown the filter to manually clean the grids, as the DE was caked on too hard to backwash.
No longer use it and have been running on the start up charge of DE all season, pressure is only up 4 psi and that's from cotton wood.
