Minh,

as you are online, you have the most powerful research tool ever created in the internet at your fingertips, so use it. Drugs.com, Wikipedia, WebMD are all sources for drug information online, using one site to check the other's reliability. With that information you should be able to ask your medical professional questions and voice your concerns over what's being prescribed to you.

I do find it humorous that you have issues using marijuana but apparently are fine with taking benzo's and fentanyl. I would take the time to look up these medications and understand each. Fentanyl is the most powerful opiate available for humans...100x stronger then heroin. When I read up on Lorazepam, it scared the crap out of me.

Anyway, as far as how long it takes for your body to readjust after the pain meds, it'll be different for everyone. It took me about 6 weeks or so.