I have been smoking marijuana for more than 12 years fairly heavily and every day, and have quit many times for varying periods.
Different people seem to have different levels of dependency, most people seem to have no problems at all or at least no major problems, however you are one of the rare unlucky ones. The longest I have quit is one year.
I have at some points had fairly severe symptoms such as diziness and shaking, confusion and disorientation..lack of apetite and been very aggitated and depressed as well as an inability to sleep. But severe symptoms like this only when going from smoking 6 or more times a day to not smoking at all and usually faded after the first 2 weeks to just anxiety and sleeplessness.
I usually have no symptoms of withdrawl at all, even going cold turkey, it seems to depend more on my mental state than anything.
the symptoms of psychological and habitual addiction only last a month or two at the very most for me, and usually not nearly that long. Residual effects of the drug can last up to 3 months as it completely clears your system though.
You may notice your mind is sharper and memory is better after about 3 months without it, so it is worth quitting if you are doing a lot of study.
I quit again last week for the first time in around 5 years without any negative symptoms. As a daily smoker, it's hard to break the habbit sometimes, so it might be good to find something else to take your mind off of it.
Hopefully after a couple of weeks it will have eased up for you. It shouldn't take long
I know some people claim to have had more severe problems, but the truth is it is mostly psychological and seeing a therapist may be the best solution.
you just need to try to relax. Chill out with a cup of tea or something when you feel really bad and just try to relax your mind.
It isn't a physical addiction as such, so how long it takes you to recover depends a lot on how prepared you are mentally. Just stay calm, try to keep from stresssing overly about it and take it easy. Don't put too much pressure on yourself.
and once again, if the symptoms are as bad as you claim, I really suggest some form of councelling, narcotics ananymous may be one option, although possibly not the best option.
You'll be fine after a short while, just remember that, and take it one day at a time. You'll be feeling fine before you know it.