For The Last Few Months, My 10 Year Old Has

For the last few months, my 10 year old has been having stomach pain every 2-3 weeks. It is worse in the mornings, but can occur any time of day. Sometimes he throws up a lot, sometimes a little, and sometimes not at all. This last case is worse. He woke up yesterday with stomach pain, threw up, but felt better by mid-afternoon. Today, he woke up and felt fine, but threw up 3 times by mid-morning. He says that he feels like he has to poop, but can't. Just now before bed, he threw up a bit again.