The commonest causes of abdominal pain are: Intestinal causes
: Intestinal causes like stomach viruses, ameobiasis, more chronic causes like adhesions, intussusception, diverticulosis, crohn's disease, etc. Organic causes
: the pain can be related to inflammation in a particular organ, like the liver, gall bladder, pancrease, appendix, etc. Genitourinary causes
: there are a large number of causes here too, like like renal pain due to stones, glomerulonephritis, ureteric stone, bladder infections, etc.
As such, a lower abdominal pain could be caused by a very large number of causes. A generalized pain as in your case is usually due to intestinal causes like crohn's disease, etc.
You should consult a doctor for this, you should consult your family physician or PCP. You will need to be examined clinically and if necessary undergo investigations like an ultrasound examination of the lower abdomen to find out the exact cause form the large number of possibilities.
You can look up here: http://www.mayoclinic.com/health/abdominal-pain/DG00013
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