1. Doesn't have a thing to do with vaping. Digestive and respiratory systems are not connected. Nothing you breath should alter your digestive system unless it's seriously toxic.
2. "Stomach" is a vague term, especially when describing pain. Your stomach is actually located just below your rib cage, but if you go laxatives that implies that your pain is in your lower abdomen. Being specific on where the pain is located can help identify the cause. Pain in the lower abdomen could be anything from constipation to an inguinal hernia. Upper abdominal pain is usually caused by gas, pulled muscle, or intestinal blockage. Since this is a recent change rather than an ongoing issue other things to consider are possible food poisoning, appendicitis, pancreatitis, kidney infection, or kidney stones.
The two things that are important here is being able to identify the specific area of pain, and seeing a proper gastrointestinal doctor. The doctor at the ER, emergency clinic, or your general practitioner really isn't good enough here, you need to see a gastrointestinal specialist. There are too many vastly different possible causes and it's going to take xrays and an MRI as a minimum to find the cause.