could be an infection...must get checked by a doctor. need more details like are you menstruating? fever? first experience?
Maybe you've got some kind of a flu, a virus maybe. Take some hot tea with lemon and honey, hope that helps, if not see a doctor
From the vague symptoms ic ould be anything ranging from bad gas t pancreatitis..
the stomache, pancrease and intestines are on the left side of your body, an exacerbation of any of those areas could contribute to your problem .. if it getsintolerable I;d head to an ED