I think this could happen. I believe you probably have anxiety/stress issues. This causes stomach pains in most cases. Even if you don't feel that stressed, yous aid you have before. It can hang around sort of mildly but you will realise you are tense and everything when you actually relax. Try to just relax all your stomach muscles. Lie back in your chair and breathe deep so your stomach goes up and down. If you can get your muscles to relax, the pain should go away. If not, something else is causing it. I believe smoking Cannabis could help you recognise this because it relaxes your muscles, but if you are tensing your stomach muscles because of stress, the tensing and pain would be even more apparent. Whereas most of the time you just ignore it.