100 mg is a very large dose, and it is suspicious that not even a little bit of it was absorbed.
It's entirely possible that there was no pregnenolone in your pills, or not the amount that the label claims.
The supplement industry isn't regulated in any meaningful way. Never ever forget this.
I know Life Extension is one of the popular brands but I personally don't trust it and don't buy anything from them. They're too gimmicky, overpriced, and they make outrageous claims.
For example, when initially looking around for a supplement brand to buy the majority of my stuff from, I ran across a Life Extension article about a "safe, proven cure for migraine." I read it and was absolutely disgusted. There is no cure for migraine, much of the problem is rooted in genetic, neurological and mitochondrial issues... and the things mentioned in the article are mostly bullshit.
Because the industry has virtually no regulation, it is imperative to be ruthless in your selection of brands. Employ a zero-tolerance policy. So for me, Life Extension demonstrated a very cavalier lack of professional ethics in their magazine's claims about an OTC migraine "cure," especially when they do not mention mitochondrial function or the glutamatergic system at all. That's enough for me to purchase none of their products; they simply cannot be trusted.
Try pregnenolone from a different brand.