You need downthrust. Thats were the nose of the engine is lower than the back of the engine. You may also have too much positive wing incedence. This is where the leading edge of the wing is too high and causes the plane to climb. The only proper way to check this is with an incedence meter.

What plane are you flying? If you don't know the name post a pic and someone will identify the model. This might also help us to help you.