Unfortunately your boyfriend is in the position of many Americans right now-- choosing between finances and health care. Be aware that sometimes people wait too long, and a simple problem becomes a more costly one. I'm not saying he needs to run to a doctor, but if he continues to have problems that should be considered.
It would require an exam to determine what is going on with your BF. The pain could be from a pulled muscle or from a hernia; in line with the first paragraph, a hernia can be a 'benign' medical condition that can become a life-threatening emergency if it becomes 'incarcerated'--i.e. bowel becomes trapped and the blood supply pinched off.
Other considerations include appendicitis or diverticulitis-- unlikely given the lack of fever, nausea, or diarrhea, but again, nothing can really be ruled out without an examination. So many things can cause abdominal pain-- bowel obstruction, kidney stones... even disc herniation can cause abdominal pain if it is a certain location.
I wish I could be of more help; I can't even say with certainty that he should see a doctor or should wait. In general, I would recommend seeing a doctor if such a condition interferes with function, if it continues for a long period of time, or if 'constitutional symptoms' appear-- like fever, nausea and vomiting, or diarrhea.