A gastroenterologist should be able to help you order the stomach tests. Their are blood test you can take for candida. You can go online as well to look for labs that do it without a Dr.'s request. I recently found a place called medlabs that uses their own doctors for referal, they send you the packet and you do the testing on your own (finger prick test or you need to find a lab if you want to do it via blood serum) . I just recieved my allergy testing with candida kit today and will try it out before spending money on any other testing they have as it is costly but not as costly as using my own insurance believe it or not. NY is overly expensive and it seems the labs have a monopoly here. The only thing is they don't do testing in some states like NY so if you life there you can't order from them. If you know anyone that lives in like NJ you can ask if they will let you use their address to order the kit.
Try food elimnations like Sugar and maybe eating very healthy for a week and see if it helps, it helped me and i plan on going back to it after i do my allergy test. its really really hard as i'm a foodie but when i think about my isolated life right now, it's worth it!