What Causes Muscular And Nerve Pain Along With Severe Constipation?

After 2 and 1/2 years of increasing symptoms and pain, I finally switched neurologists and am now under the care of the Chief of Neurology at a well renowned hospital in IL. I also have been with the same psychiatrist for 14 years. I was horrified to learn in June or 2014 that my Guillain-Barre Symptoms have returned, most likely for good and are much worse than when I had it 27 years ago. I have also had serotonin syndrome 5 times, as I have chronic migraines and MDD, recurrent, severe and treatment resistant. I have many other conditions, including IBS where I alternate between constipation or diarrhea. My IBS is stress related, rather than my diet as I don't have one. My concern is that I lost my appetite when I had SS the first time. I have to force myself to eat and rely on using Ensure since then. The diagnosis has been so devastating, that I haven't eaten more that a granola bar, yogurt or a banana in the morning and that is it. I've been doing this for four months. So while I'm not eating, I weigh more than I ever have and my stomach gets so bloated, I have such terrible cramping and pain and I often look like I'm pregnant. My sister lost a friend to ovarian cancer, and her first noticable symptom was that she too looked pregnant. Should I be concerned that I may have it? If so, what steps should I take? Additionally, what other things might be causing this? I also have skeletal, muscular and nerve pain and am in pain every day. I'm just looking for a second opinion. I was placed on SSA disability late last year and have been navigating through understanding Medicare and Medicaid. I currently do not have a primary doctor, due to my new insurance. I've discussed it with both doctors, but there are other things that are more urgent in their minds. So, any advice would be appreciated. Unfortunately, I have lost too many friends and family to cancer. In all cases, there daily pain was attributed to another condition. By the time the cancer was discovered, it had already metastasized to their bones. I don't want that to be my story. Thanks in advance for your consideration.