I feel you about the dreams man, they fucked with me bad for a long time after I stopped cooking/using meth. For the first 5 or 6 years of my bid, I'd have dreams about cooking and or shooting dope at least two, sometimes three times a week. A lot of times they'd have really fucked up, garbled family themes as well. And in the ones where I was shooting meth, they'd be super realistic. Like I'd see the light flash off the bevel of the needle as I found it to orient for the shot, I'd feel the sting as it penetrated, feel the scar tissue pop, register and get high in my dream, and as soon as the plunger hit home I'd always wake up, bolt upright in my bunk. I'd feel a ghost high for like five seconds, but the dreams were so realistic I could still taste that shit when I woke up.
But it finally stopped. The desire to use didn't, that didn't go away until I gave in, put myself out there at warp speed and fucking traumatized myself lol. Are you still taking the mirtazapine at night? I know a lot of people report crazy ass dreams when on that, I know I did lol, but I enjoyed mine. I described them as "acid nightmares, but in a good way" Might be a good idea to give that a rest though, if you're still taking it, see if that helps?