Hello all!!!!!!!

I have been having problems with constipation, lower left side pain. This pain only happens when I start to feel cramps like I need to have a bowel movement, then it feels liked thigs are :locked up". I vomit (without nausea), and usually soon after I have a watery bowel movement. Sorry to be so graphic but I dont know how else to explain it. Then after several trips to "empty bowel" , I feel weak and exhausted. The pain is unbearable only initially, until I start passing stool. It feels as if I need to mash around on my left side to get things going but it is painful. I had a colonoscopy, EGD, and CT of abdomen and everything was ok, except I had a narrowed sigmoid colon,and my MD told me to take MOM(milk of magnesia) every other day. It appears that my symptoms are getting worse and I wanted to talk to others with the same problem. Does anyone have any advice?????????? Thanks!!!!!!