MSPI vs oversupply vs infection?

3litttlebirds

When testing revealed blood in LO's poop, the pedi said it was likely a milk intolerance and possibly soy. I have since read that an oversupply can also cause blood in poop. I know I used to have an oversupply when I EP'ed...not sure about now that EBF. I know I still have a forceful letdown and strong flow even after the letdown, despite weeks and weeks of block feeding (actually LO mostly nurses on one side only all the time...has trouble latching on other side). And now today my DH's coworker said her LO had blood in her poop due to a virus. 

So my question...did anyone else's pedi do any testing to see if there actually is a milk/soy intolerance? Is there even such testing? Did your pedi do testing to rule out a virus? I'm wondering because it's kind of a lot to change your diet if that's not what's causing the blood. And if something like a virus is causing the blood, I'd like to know, so it can be treated. I'd like to be on the right path from the get go, if there actually is any way to test for sure, rather than just assuming. So many things have the same symptoms...