I am having problem with left hypogastric pain ( left lower abdomen) it's discomforting while I am menstruatin

the pain I feel is right in my back where rectum is located, I feel pain whenever I need to p gas or flatus, its so intense and sharp that I actually lose my conciousness. when I feel the pain it stops me doing anything, I cant move myself and I need a support to hold. my whole abdomen becomes tender and I can feel the discomfort all through out the 5 days of menses. after menses, the pain usually doesnt feel every day, sometimes it feels daily and sometimes its not there for 1 or 2 days. I hve been constipated on and off even though I am eating raw veggies and fruits but still I am having this constipation. over all I feel tired and fatigued with headache and other body aches. this time I saw my doctor, she did digital rectal exam but it was unremarkabale. what is the underlying cause, I am just 26years old.