Sounds like something is way off!
If your cg is correct and assuming your wing rigging is also right,the tailplane or flapperons would be next to check.
Is your stabiliser flat or is there a twist?
This can be adjusted by the two rod ends(leading edge up to bring the nose down)
The forward mount may be adjustable , if it is safe to do so you could re drill the bracket?
After checking for twist ,test fly
I have found the best position for the flapperons in level flight is to sight against the horizon.
Anything more than few degree off creates a lot of drag.
The non symmetrical flapperons are very efficient at bringing the nose down but not so good the other way and would be very noticable
If your pitch changes significantly with power check your engine thrust line