There can be a large number of causes for pain lower abdomen. This could be simply due to something bad that you ate which is causing pain in the gastro intestinal tract. You can observe it for a day or two, it should usually subside by then.
For now, you should try with:
Take OTC painkillers like Motrin/Advil one tab 8 hourly to control the pain. You should take it after food as it can cause gastritis. If there is any gastritis, take OTC Cap. Prilosec one cap daily.
Lots of fluids - water, juice, Gatorade.
Avoid smoking, cut down on alcohol, cut down on caffeine
High fiber diet -vegetables, fruits, non processed meat and fish - be sure to take nutritious diet
Avoid fatty fried foods
Maintaining regular bowel movements at fixed time
Regular hours of sleep
Regular exercise - take 30 minutes of walk 5 times a week.
This will help to regularize the system, but if the symptoms persist show your doctor for further investigations.
Lower abdominal pain in men can have many causes:
Intestinal causes: Intestinal causes like stomach viruses, ameobiasis, more chronic causes like diverticulitis, adhesions, intussusception, ulcerative colitis, Crohn's disease, Irritable bowel syndrome, 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.
Muscle pain: due to muscular trauma during exercise, sports, etc.
As such, a lower abdominal pain could be caused by a very large number of causes. In most cases it is due to some simple GIT problem like intake of some injurious food which causes spasms in the intestine and pass off in a couple of days. If symptoms persist, 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.