Most archers have a problem with a flyer at some point in time. As someone above suggested, mark your arrows to determine if it's an equipment problem. If it is, it's repair or replace.
If it isn't an equipment problem, it's shooting form and almost every archer has had to deal with this at some point. Try this, it may help:
First, cut down on the number of arrows your shooting in each set. If working on form, I suggest shooting only two. One fletched and the other bare shaft. The bare shaft will pick up even the smallest form problem.
Next, in my experience three common shooting form problems can result in a flyer:
1. Plucking the string on release. This is caused by jerking the hand away from your face when releasing the bow string. I find that my fingers just slide along my face when my release is correct.
2. Canting the bow. The further you cant the top limb of the bow to the right, the further the arrow tends to hit to the right. Make sure you're canting the bow at a consistent angle with each shot. A flyer to the left can be the result of tilting the top bow limb further to the left on that shot.
3. Jerking the bow arm to the left on release. If you move the bow arm during the release, the arrow will move in the same direction.
String plucking and bow arm movement can result from fatigue. Remember, it doesn't matter how many arrows you shoot with each practice. The key is to shoot each arrow well. If you begin shooting poorly, take a break.