What Causes Constant Stomach Infection And Chest Pain?

Hi, my seven year old son has been complaining of feeling sick for a couple of months. It all started with the feeling like he was busting to do a wee and when he tries to go he cannot. His urine was tested and there was no infection. He is Lactose Intolerant. He feels sick in the stomach and in his chest. He was advised to take 3mls of Mylanta in the morning in case he had reflex. This doesn t seem to have completely solved him feeling sick either. I ve started him on a gluten free diet although he was gene tested and does not have the Caeliac gene. I think this is helping but he is on and off still feeling sick. He mainly feels sick in the morning before school and I do think that there is some anxiety about going to school, but I m not sure if this could cause his symtoms. I visited his school today and during the lesson he told me that he felt sick and his face was pale and lips a little white. Again this has happened in the past but not recently. I d like to know what the next step should be or weather these symtoms may lead to information on what may be wrong. I m thinking he may need a blood test ? Thanks for your help.