Why do I get bad lower back pain when I need a bowel movement.?

Unity of structure. Your body is one unit. Your intestines hang from your lower back. There is overlap in nerve supply. People who are chronically constipated can easily get back pain. As precaution, If you have other medical problems, or a family history of colon cancer, get checked out by a doc in person. Make sure you've had a recent gyn exam too. I hope you feel better.
Colon spasm. I suspect that you are experiencing "referred pain" from your colon, which will go into a bit of a spasm to expel its contents when it is time for you to defecate. If this is a new problem for you, it might be wise to check with your doctor to ensure it isn't something else. You might also see if an OTC stool softener like Docusate might relieve the symptom somewhat. .

Related Questions

I just recently started having lower back pain on both sides only when I have a bowel movement. What could it be?

Disc herniation. Hello: Pain with bowel straining might suggest a herniated disc. Discs hurt with sitting and straining (Valsalva). You might want to get examined by a physiatrist specialized in spine care. Read more...
Muscle pulling or nerve pressure. This could be muscle pull or pressure on the nerves in the back. Your physician can help clarify. Read more...

Hubby having lower back pain and sometimes front pain below ribbs in early morng which wakes him up. Pain goes away after bowel movement. Sleep posture?

Needs a Physical. Your husband needs a physical with labs to start to figure out why he has this pain in the morning. Most concerning would be cardiac, but this could also be gastric reflux . Need more information, exam , labs and EKG. Read more...

I think I'm having more bowel movements recently and feel gas and lower back pain when I do. Is this something to be worried about?

1st, why RU gassy? Feeling full of "gas" may reflect malabsorption of food (like gluten, lactose), intake of poorly digested food, or choosing foods known to promote gas (beans, fizzy drinks). Sometimes its more complicated--a stomach emptying too slowly, bacterial overgrowth syndrome, delayed intestinal function, partial obstruction from any cause, infection, rectum problems, and pelvic pathology outside the gut. Read more...