"Also, what brand niacin and mg should I start with?"
Watch some vids first. It's a test, not a treatment. It will even make your BP go down temporarily and possibly dramatically, so you should be wary. Or maybe don't do it at all.
"In 6th grade, I literally didn’t go for two weeks and finally told my mom and after 2 or 3 enemas I finally went.. during pregnancy was terrible!!!!"
Problems with gut bacteria, which you have, can lead to heightened inflammation bodywide. That worsens the mast cell problem. Did you have a CRP blood test?
How old are you?
"Because I always get too constipated with pain meds. Like I can go week plus days without Bm if I take pain pills... " Okay, that's because opioid type painkillers stop movement in the gut (peristalsis). But if you're more sever than average, why? Maybe lack of good gut bacteria. Maybe. Some people get horrible health because of that, especially after many bouts of Abx.
...and angioedema is usually associated with rashes (urticaria). But you don't mention having rashes, so that's a clue. Of something.
Keep your chin up, we're making progress in Dxing :)
"I didn’t even take pain meds after gall bladder surgery.. except for ibuprofen." Why was that?
homocysteine = Hcy
Is your pulse rate high? If you get dizzy because the water in your blood stream is leaving and going into tissue, that makes the heart beat faster to compensate.
Please research to find any association of your meds with angioedema.
Got to go for now...