I am not giving medical advise. you should consult your doctors as to their recomended methods. dont self diagnose
this is what I was told to do in dialiating. [ 15 years ago ]
pre warm the dialiator in warm water, not hot water. cold causes muscles to tighten up. use a comfortable size dialiator, apply generous lube. Schrang recomended a surgical lube. those lubes are designed not to 'dry up or get sticky' so quickly.
insert and remove slowly, two or three times. that assured full spreading of the lube.
take the next size up, lube and insert. after the muscles relax, push the handle end down toward the anus, and hold. release after a few minutes, rest and repeat.
dialtion sessions were every 4 hours, for 20 minutes.
in the early days just after surgery, i was restricted to using just the smaller dialiators. maintaining depth was the goal. about a month in, the next size came into use.
there was always caution urged not to push to far or too fast. ' let pain levels be your guide' was his motto. there will be discomfort, but you should not have severe pain.
the old style dialiators we got at the hospital had 5 " tools ". the biggest is huge, and honestly, its never even been attempted. { If a guy is that big, Im running

}
again, consult your doctors for recomendations and their prefered methods.