Do you have a smart system/method to track things in your life?

I wonder what kind of methods/systems people use to try and track certain things in their life, and what is some of the things they're tracking.

One example of mine is to try and track how well I'm generally feeling, and related- whether, and how certain supplements and vitamins affect that.
Another example is how often do I get physical minor-medium inconveniences (that I generally live with), such as stomach aches, back pains etc, so I can potentially try to figure out what's casing them.

I was really struggling to find a solution to this and I wonder what other smart systems people have.

Full disclosure: I'm working on a project trying to provide a cool solution to this (that's the sysytem I use) and was hoping to learn more about the subject from others.