You maybe pushing into the pistol as the trigger breaks in anticipation of the recoil. Try these exercises
1-Get several dummy rounds and without looking, load them mixed in with live rounds, then keeping you eye on the front site fire the rounds. When you hit a dummy you should be able to see what the front site is doing-(down, Left, right etc....)if so go to the next step to cure
2-Practice just dry firing your pistol focusing on your trigger squeeze and sight alignment until you consistently have a clean break (probably over 500 repetitions)
3-Then go back to firing with the dummy rounds to see if you have cured your issue , if not go back to the dry fire practice and repeat
Make sure your using a good firm Highhanded grip, your trigger finger should be pointed naturally forward to your target and both thumbs should point forward. If your unsure about your grip let me know and I will find a link for you
Good luck your starting at the right place
Bob