People are often asked to keep a food diary alongside treatment and almost immediately abandon it, for a good reason: a complete record of everything eaten is a second job, and the detail that gets collected is rarely the detail anyone needed.
A narrower note works better and survives longer. The goal is not a nutritional audit. It is to be able to answer one question later, which is what tends to precede a bad day.
Log three things and nothing else. What you ate in the two hours before any symptom you noticed. How the symptom felt, in your own words, and roughly how long it lasted. Where you were in the dose cycle, meaning how many days since the injection.
That last item is the one people leave out and the one that carries most of the signal. Symptoms that cluster in the day or two after a dose and fade later are a different pattern from symptoms scattered evenly through the week, and the difference is invisible unless the days since dose is on the row.
Use consistent words. If you write queasy one week, nauseated the next and off the week after, you have three symptoms in the record and no pattern. Pick four or five terms and reuse them. A rough one to five severity number alongside is enough, and better than an adjective, because you can scan a column of numbers.
Do not log the good days as nothing. Log them as fine. A record with entries only on bad days makes every week look bad, both to you and to whoever reads it.
Two weeks of this is usually enough to see a pattern or to rule one out, and then you can stop. It is a diagnostic exercise, not a permanent habit.
I keep these notes on the same rows as the dose entries in Peptide Tracker & Calculator, which is what makes the days since dose figure automatic rather than something to count out on your fingers.