So where is the evidence?

After taking gabapentin, I ended up with all the symptoms attributed to this 'Candida' business:
- intestinal bloating, cramping, burning and malabsorption, IBS symptoms
- flu symptoms and sinus problems
- crippling fatigue
- feeling like my skin was crawling
- itchy rectum
- depression, anxiety and other psycological problems
- yellow/green tongue
- white bumps on the back of my tongue
- brain fog/ a feeling of being drunk all the time(in a bad way)
- chills, a basic unwell feeling
- dry and cracked lips and hands

the Dr's couldn't find anything. I tried medication for Giardia, more Antibiotics etc but nothing worked. So I decided to stick myself on the candida diet, tried Nystatin (did nothing) and am now taking diflucan (did something). My symptoms have both flared and reduced at times so for the last week and a half I decided to get even stricter and go on the caveman diet, I'm still taking diflucan as well.

My question is- where is the evidence of candida? Where is the test that shows it? A colonscopy should show it, yet the threads on the subject have people saying 'it looks like mucos' are you serious? All I've read on this site so far is dogmatism from people who are 'sure' that they have it, their only evidence being that these collection of symptoms 'must' be candida or that their treatment plans worked on them so it must have been candida?