It is quite usual to forget certain things in our day-to-day life. There can be various reasons why we forget simple things, for example your attention was focused on a different thought, lack of sleep, stress, handling too many things at the same time, nervousness/anxiety etc. One way of remembering things or making sure that you don't forget the important ones is to write them down in a diary, like a to-do-list or day planner etc. It would also be beneficial for you to engage yourself in activities/games that require you to remember things and practice your memory skills (you can check this link for few suggestion especially the one with playing cards, which I would personally recommend). It would also be good if you take out time 20-30 minutes everyday or 3 times a week or even once a week for a start, for exercising or meditation, or simply a walk followed by deep breathing. This will be helpful for you to lower stress levels and take a break from everyday busy life.
I hope you find these suggestions helpful.