What Causes Severe Pain In Abdomen Along With Vomiting?

Hi I have been vomiting for the past 4 weeks yes 4 weeks!! I have this severe pain in my stomach its like a popping sensation like when you pull and elastic band and let it go... I have had blood tests done and they did not show up any signs of infection .... And CTS and MRIs are all clear ... Every time I eat I get sick.. When I walk or laugh or sometimes Just lie still I can feel pressure and than the pop! Please help me I m 14 years old and I can t carry on like this