Hmmm. Just run a google search.

weed withdrawal stomach aches - Google Search

Not the best one, but in there you see loads of snippets "get stomach pains when I quit smoking weed", "WITHDRAWAL SYMPTOMS... STOMACH ACHES" ... heres a more specific link marijuana withdrawal, Marijuana Detox & marijuana withdrawal symptoms by addiction withdrawal.com

Marijuana withdrawal is very real. I have no idea where the common misconception that "you cant withdrawal from weed" came from (probably from dumbasses). Weed addiction and weed withdrawal are all too real for some of us, shiiiiit.

It definitely is from the cannabis. I started getting morning stomach aches, I'd say after being an every day smoker for 4-5 months. Many stoners I associate have the same routine; wake up with no apetite and a stomach ache, blaze all day, eventually eat a ridiculous amount of food in one sitting, go to sleep and start over. A lot of people agree that the morning stomach ache almost feels like last nights munchies busting out of your stomach (the results of such an irregular diet). A friend of mine described the feeling perfect; "when I wake up I am way too fucking grossed out to even take a bite of toast". Then the herb takes the pain away and stimulates the apetite.

So essentially weed supresses my apetite, since I have trouble eating without it. I have a friend whos been an every day smoker for well over 2 years, and he is sooooooooooooooo skinny. "I only eat once a day man, and its usually small. I just never ever ever have an apetite". Its all from his herb problem.