Hi Ruby
I've had much the same problems as you for the last 3 years. I was very active and able to live a normal life, then one day at work I got a pain in the centre of my back, which progressively got worse. Went to the doctors and was initially diagnosed with a popped disc, for which I was told to rest. After a week there was no improvement with the back pain, so was referred to see a physiotherapist, however each appointment was hopeless as the pain in my back was stopping me from being able to do exercises the physio asked me to do. One appointment, the physio told me to get my doctor to prescribe Naproxen to alleviate the pain and allow me to start being able to do the physio exercises. My doctor prescribed me some Naproxen and within 2 days of taking them I had intense upper abdominal pain, the feeling like something was tearing the top of my stomach apart, it was horrendous, and along with other symptoms I was getting at the same time, rapid heart rate, sweating, shaking, I really thought I was dying! I went back to see a different doctor who told me to stop taking Naproxen and put me on Omeprazole, and within a day the severe upper abdominal pains stopped. Unfortunately, I have developed a whole host of symptoms, including the ones you have mentioned and experience, and been diagnosed with Fibromyalgia, CFS/ME, Gastritis, IBS, Anxiety and Stress Related Disorder.
Referring to your questions, I too have had 2 faecal calprotectin tests done in recent months, both were >300, with the first being >1400. It took me to request these tests to my doctor, if I hadn't we would still be in the dark and suffering unnecessarily, and I am now being investigated for Crohns / Ulcerative Colitis. I recently had a colonoscopy, and the procedure and biopsies came back normal, which has in turn ruled out Ulcerative Colitis. The next step for me is a small bowel MRI on the 16th January to investigate for Crohns. Calprotectin tests can give false positive results, and this usually happens when you take Ibuprofen or NSAIDs, or you have a stomach bug or food poisoning. I don't recollect having any of these so I'm guessing my calprotectin results are positive because there is a problem going on inside me, so yes calprotectin tests give positive results for other reasons.
As for where you go from here, that's a question I'd like answered for me too, I've had every test under the sun done on me, and they have all come back normal, apart from slight raised white blood cells a couple of times, high faecal calprotectin results and low vitamin D levels. Obviously the next step for me is the MRI, but after this, I really don't know. I hoping the MRI comes back fine, but there's a part of me hoping that something shows up, it would be nice to have some answers after 3+ years.
BTW, my rectal bleeding and blood in stools was caused by rectal polyps and internal hemorrhoids.
I do wish you all the best and I'm sorry I can't give you any definite answers, the only advice I can give is be prepared for a long haul for diagnosis, as digestive issues are some of the hardest to diagnose.
Take care and keep in touch with any developments.