first..... look at your technique, are you "pushing"? very common to push the trigger, usually result in a low left group for right handed shooters. this is the problem almost always.
second.... clean your gun, look at the parts for uneven wear or bad machining that would put pressure on the barrel, look for shiney areas that are not uniform.
next your pt845 has fixed sights, so your adjustments are limited. you should be able to pull the rear set screw and drift the sight with a dowel while the slide is in a vise, the reset the screw..... this will give you windage but not elevation. once you get the group centered at 6 oclock you can adjust your sight picture to increase elevation.