Tuning is paramount to getting good arrow flight. Sounds like you're new and need to learn stuff. Maybe you got lucky and your first set of arrows shot OK. When you change something like fletching the dynamic spine and balance of the arrow can be different.
As for tuning? You need to learn it. One of the best guides I've ever come across is Easton Archery's Tuning Guide. You can find a copy at
www.huntersfriend.com or at
www.bowjackson.com.
It does a good job of explaining such simple things as how to install and set up rests up to and including broadhead tuning. All in fairly simple terminology, I might add. You learn the lingo and then the process and you'll be on your way to happier shooting days.