I second the advice, and suggest Anki SRS software https://apps.ankiweb.net/ https://apps.ankiweb.net/ for remembering what you have studied. I have a differen

I second the advice, and suggest Anki SRS software https://apps.ankiweb.net/ https://apps.ankiweb.net/ for remembering what you have studied. I have a different problem, not just it is difficult to study simultaneous subjects, but due to family or professional duties, sometimes I spent sometime without studying it I feel that I forget a lot of stuff. Anki helps me stay sharp and space more my study sessions.