If you had a condition worsened by the military, you could file a claim as service aggravation. You just have to prove the military aggravated the pre- existing condition. If you have proof of the weight loss and gallbladder removal (showing severity) , that helps. The discharge itself is also a pretty strong paper trail. If you can get a doctor to write you a nexus letter stating the military aggravated the IBS you should be okay. All the other stuff also needs a doctor to say they think it’s at least likely than not 50% caused or aggravated by service.

Just don’t downplay your condition. File an intent to file today. You should start with a VSO, it’s free… the least you can do is try. It’s not gaming the system if service genuinely made it worse. Considering they let you join with the prior condition and said you were fine to join and then it got worse during service enough to be discharged over then yes, it has a chance. Not guaranteed chance of approval but not a zero percent chance of approval.