It sounds like your CG is too far forward. Do the dive test: Climb fairly high and dive straight down at 1/4 or less throttle. Let the elevator stick go to neutral. The plane should continue straight down or pull-out very gradually. If it pulls-out fast, the CG is too far forward and you can add tail weight (1/4 oz at a time!)

You should always make sure the basic alignment and control system of the plane is correct before making changes to the CG.