I'm slowly gaining my depth back from similar loss as yours. I had a solid 5" leaving the hospital, but lost a lot, maybe as little as 3.5" depth (had some bad swelling early in recovery)
Just keep gently pushing harder using static pressure and slight rotation back amd forth, about a quarter turn in each direction while pressing as hard as you can tolerate without causing too much pain. I use different diameter dilators, the narrower ones work better for getting initial depth, then dilating further using larger toys as needed.
I'm probably 3-6 months from getting back to the original depth and hopefully it will stretch even further. but I am also trying to get more width also. It gets sore when I push it, so usually I only stretch every few days or until I am no longer sore, accounting for sex, because I don't want sex to be painful :/
good luck!