How old are you? Have you had a colonoscopy?
You're on a lot of medicines; some of which cause bleeding. You might have a small, slow internal bleed. The blood can irritate the lining of your abdomen and may cause the shoulder pain, and of course, the low blood count.
It seems that you need a thorough workup. What you're describing may not be related to your wls surgery, but, with the passage of life, is due to some other medical condition: ulcer, perforation; small bleed, cancer, hemorrhagic cyst; a pancreatic lesion; other.
Get the CT scan, for sure; hope it's of your abdomen and pelvis. Full battery of blood tests and a good exam. An MRI might be indicated, as is a colonoscopy, and possibly an upper endoscopy (looking down your esophagus and further, as far as possible).
You're doing the right thing to check on it. Hang in there.