I don't think probiotics would cause a bad reaction if you had SIFO because probiotics don't kill fungi so much as crowd them out. One of the fastest and easiest ways to see if you have candida is to take a fairly large dose of antifungals and see if you have die-off symptoms. If you do this, do it on a day off from work where you can lay down all day if need be. Whole Foods sells a product called CaprilyCare which is mostly caprylic acid (a fatty acid found in coconut oil). Take 8 of those (this is a normal dose, it is a food more than a drug) on an empty stomach and see if you feel anything (burping, runny nose, brain fog, etc.).
Great Plains Laboratory has a test for candida. I don't know how much it costs because you have to register as a patient to find out. Look here: