Download a symptom tracker or patient care app and record food, sleep and supplements etc for a week. Have it auto correlate what it could be or use the logs to determine what it could be yourself. For me it was sleep, not exercising and Distressed mood that caused me to have such days.

Try One of these apps(all have free basic functionality afaik) symply, careclinic, or foody if you suspect it’s food related gl.