What might be causing my symptoms?

26M. I've been dealing with abdominal pain and other issues consistently for over a year at this point and I haven't been able to get any good answers from doctors and the tests/scans they've had me do. Does anyone have an idea of what might be causing these symptoms?

Symptoms:

- Sore/tight upper abdominal pain

- Pulsing/twitching in my stomach

- The right side of my neck and shoulder is swollen, and gets worse when my abdominal pain is worse, but seems to constantly be at least slightly swollen

- Lightheadedness

- Fatigue

- It affects my breathing and it's harder to get a full breath when the pain gets worse.

- My symptoms get worse when I'm warm (such as in the shower, or outside on a hot day). And also when I lay down on my left side

- Occasionally it will feel like my stomach "drops" and I'll get very lightheaded and dizzy, but it only lasts for a few seconds

Test/scans I've had:

Abdominal ultrasound and CT

Endoscopy and colonoscopy

Neck ultrasound and MRI

Celiac panel

SIBO test

H pylori test

Loads of bloodwork