I am NOT a doctor and I am NOT offering you any advice. Just gonna share some of my story, since its a bit similar to yours. Since you mentioned PTSD, I'm guessing that your're getting your medical care at the VA, same as I do. The past couple years I went thru Trazadone, Zoloft, Cymbalta, and Effexor, with Lorazepam on the side for the tough moments. None of that really "worked" for me to eliminate the symptoms of sleeplessness, anxiety, panic attacks, harsh nighmares, etc. Basically what I noticed from the meds was it made me sleep a lot more, and I felt half asleep when awake. It made it a little easier to get thru the day, cuz I felt like I was in a stupor from sleeping too much. But all the panic triggers were still very much operating.
At the time I started seeing the shrink and taking the SSRI type meds, I had not smoked MJ in many years. About a year ago, I started toking just tiny hits of MJ, just to see what it would do. FOR ME, it seemed to work great, and I didn't notice anything wierd from mixing with the SSRIs. I had the idea to discuss this with my shrink, and have him help me along with a trial to ease off the script meds, try the MJ on a 'controlled' basis, and for him to chart my progress. I live in a NON-MedMJ state, so I was thinking doing this would help me prepare a "medical necessity" defense if I ever got busted. I had less than cooperative results from the shrink, and he offered to start me back on the Lorazepam to help me get myself together and back in my right mind. I've since stopped seeing the shrink, have eased myself off the SSRI meds, and do only MJ now. I believe I'm seeing some very postive results from the whole thing. I also have a lot of pain from prior injuries and the MJ helps with that real well, also. My only med at the present time is MJ, I sleep well, manage the pain, and my "emotional" state has improved greatly with the PTSD, panic, anxiety issues, etc.
I would encourage you to be open and honest with your doc, and tell him what you think and what you want to try. I hope that your doc is easier to get the idea across to than mine. If you've only been on the Zoloft for a couple months, coming down off of it should not be too intense, but those SSRI type drugs can mess with your head if you cold-turkey them. If you cannot get suport from your doc, and you decide to quit them, at the very least, read everytyhing you can find on the web written by MDs, and try to make some intelligent decisions. What I decided was an extremely slow down-dosing over a period of several months to get off it. It worked for me, but I still can't recommend it to anyone else. Try your best to get your doc on-board with the idea, and keep in close touch with him(her).
Good luck.