You seem to have ruled out a lot, but you don't mention seeing a cardiologist to rule out any heart issues which would be rare at your age, but with your symptoms......worthwhile. You should also see a Gastroenterologist to determine what the pain is in your side, along with the diarrhea. Did your doctor take your BP sitting and then when you stood up? If your BP is dropping when you stand, it will cause dizziness and weakness. This can be due to dehydration, so make sure you are well hydrated with water, Gatorade and orange juice, these replace your electrolytes. But it needs to be determined if this is happening by your doctor, and why. Once you've ruled out all other causes, it's time to address this as being anxiety. It may be stemming from the break-up of your marriage. Anxiety can and does present with many of these symptoms, and you are certainly not alone. It you read some of the posts on here you will find many who suffer like you are. But all of this can be controlled with medication and therapy, and much of it can be resolved with therapy. But therapy can be a lengthy process and you need some relief now! Contact a psychiatrist for an evaluation and so the two of you can determine the best course of treatment for you. I recommend a psychiatrist because they are most knowledgable with the medications for this, and can refer you to the proper therapist. See the proper doctors regarding your BP and the pain in your side, and go from there. If your doctor was aware of how you feel upon standing, I'm sure he took your BP sitting and upon standing. If so, what did he say? Your not alone, we're always here for you to talk or just vent. Keep us posted on how you are doing, and take care.
If you've had lab work, cat scan and other medical checkups and the doctors have not found anything physically wrong then its almost certainly an anxiety/panic disorder. It sounds like you might be hyperventilating as well. Anxiety can cause so many symptoms but find a counselor to determine the fears you suffer from. Again I am assuming you've had a thorough medical checkup.