The bigger question you should ask yourself, is what are you hoping to gain by tracking? I mean if you were getting results from Google sheets you would be using it today.

If you want to make it a product you need to do it in a way that makes people less paranoid, allows them to enjoy their life, doesn't try to guilt or game them into staying involved, doesn't have, lots of notifications and makes their life better as a whole. I mean it's not healthy to think about your illness 24/7.

Those are good questions, and to answer them you really have to think about what it is to have an illness that requires treatment.

Typically you start on a medication. These usually take anywhere from 3 to 6 months to really work. Along the way you will have ups and downs, and maybe some unexpected new things happening that are related to the disease. Do you feel better today than 3, 4, 5 months ago? Are you having more sick days, fewer sick days? Are you having more or fewer days with nausea or headaches?

After being on a medication for some time, you might have a general feeling about whether it's good or not. But for people like OP, it's very often not the case that you start on a medication and everything is good. No: you go through one medication after another. Sometimes multiple stacked on top of each other. Each medication takes months to kick in.

Who remembers if medication 1 worked better than medication 5, four years later? It's surprisingly hard to remember how you felt physically. It's also really important to keep a journal of the basic facts, like what doctors you saw and what tests were done. But I think tracking how you feel is important. It allows you to compare (not scientifically or perfectly, but well enough) over time. It allows you to see trends you might not spot otherwise; a medication starting to fail as opposed to random flares, for example. Or if you track what you eat, you might notice that some types of foods make you feel bad for a couple of days after, a connection that's often hard to make without doing a full elimination diet.

I recommend people with chronic illnesses keep a spreadsheet of how you feel, day to day. But also track every medication, every switch, every diet change (if applicable), every doctor's visit and treatment decision, every symptom and side effect. I don't think anyone should obsess about it, but recording some basic facts doesn't hurt and doesn't take much time, as long as can remember to keep it up.