I've had these withdrawal symptoms time and time again in quitting pot. Yet, I still find myself going back to it eventually for whatever reason. I believe I'm quite experienced in dealing with these symptoms now, but this next time quitting is going to be really hell... I've been smoking daily for 6 months now, and am probably going to attempt quitting soon again.
Here's some helpful things you can take to alleviate some of the symptoms. Please look these up yourself and research the benefits/risks of each, as some people may have certain health conditions to prevent taking them.
5-HTP - If you're feeling depressed, this helps to give your brain more building blocks for seratonin. It also can help alleviate insomnia.
Melatonin - This hormone can also help you get to sleep (for me the insomnia is the worst part, because the less sleep I get the worse all the other withdrawal symptoms seem). Make sure you don't take it for too long, as your brain may stop making its own melatonin after some length of time.
Kava - This helps to alleviate the anxiety (and boy does it work!). It even has an interesting reverse tolerance curve, so the more you take, the less you need to get the same effect. If you drink daily or have liver problems though, this can also be hard on the liver, so I'd recommend quitting drinking, or not taking it if your liver isn't up to par. (I get mine from nakamalathome.com ) The instant kava is good for portability, and the actual root powder is very effective (but yucky tasting). Gotta have a stomach for this one, or mix the powder with apple juice or something. I highly recommend this, but be careful about the health warnings.
D/L Phenylalanine - Haven't tried this one myself yet, but have read that it helps your brain to replenish dopamine, and norepinephrine in the brain. (Might help, gonna try it this next quitting time)
Theanine - This one also helps with anxiety and can calm your brain if you get rapid thoughts that prevent you from sleeping like I do. It's basically tea extract without the caffiene. "Suntheanine" brand is clinically proven to work. Very safe, highly recommended.
Vitamins!!! - Vitamins C, B2, B12, Zinc, etc... Vitamins also help your body and mind to replenish brain chemicals and have many other benefits.
Cranberry juice - Helps to cleanse your body of toxins.
NAC (N-acetyl Cysteine) - Super antioxidant. Helps to cleanse your body (and lungs!) of toxins. Look for little juice bottles by a company called "function". The ones you want are "Urban Detox" or "House Call". They both have NAC in them, among other helpful supplements. Plus, if you're sick, the second one also helps with that.
Hope this helps ^_^