I am so so sorry for your suffering. I know that feeling of pressure. I have it myself. It's awful. You feel like you want to go to the toilet. I have a suspicion that you may have bowel obstruction. Have you had a colonoscopy? And an endoscopy to get more information.
I learned that my sigmoid, which is a thicker part at the end of your bowel is angulated, which means it folds over on itself. I've also got Scare tissue around my intestines from surgeries that creates bowel obstructions for me. I don't know if you've had prior surgery?
I don't wanna make this any more confusing than it is, but I'm just giving you my own personal experience. I've been dealing with this for 10 years now I did have surgery once to cut away scar tissue and it helped a lot. I'm wondering if they need to go in and take a look, but first of all have your colonoscopy and endoscopy first keep pushing for this. You have to become your own research specialist. I wish you all the best of luck God bless you.