Praise be to Allah.
Perhaps your forgetfulness – or your weak memory – is a result of giving birth, as your doctor said. This is not something to worry about. Or this forgetfulness may be caused by sin, because sins result in punishments that affect the heart and the body. Imaam Ibn al-Qayyim (may Allaah have mercy on him) mentioned more than sixty punishments for sin in his book al-Daa’ wa’l-Dawa’.
So if a person feels that he is losing some blessing, he should hasten to repent to Allaah. Allaah says (interpretation of the meaning):
“That is so because Allaah will never change a grace which He has bestowed on a people until they change what is in their ownselves”
If a person makes a promise then forgets it unintentionally, there is no sin on him, because Allaah has forgiven this ummah for what they forget, as is indicated by the texts. For example, the last two verses of Soorat al-Baqarah (interpretation of the meaning):
“Our Lord! Punish us not if we forget or fall into error”
And Allaah has said: “I have done that.” (Narrated by Muslim)
There are also means that will help you to remember appointments, such as using a diary (in book or electronic form) to record appointments by day and date. This is a means which is proven to work. How many people forget their appointments, but they organize them by using these reminders.
Another means is using an electronic alarm clock or a mobile phone to remind you of the time of an appointment… and other modern means that are available.
There are also audio reminders on which you can record appointments and it will speak to remind you of the appointment.
Each person must pay as much attention as possible to this matter, because breaking promises is one of the signs of the hypocrites, as it says in the hadeeth: “There are four characteristics, whoever has them is a pure hypocrite, and whoever has one of them has one of the attributes of hypocrisy until he gives it up: when he speaks, he lies; when he makes a pledge he betrays it; when he makes a promise he breaks it; and when he disputes he resorts to obscene speech.”
(Narrated by Muslim, 53)
Keeping appointments is one of the signs of the people of faith.
Similarly those who miss appointments for a reason such as that mentioned in the question should explain their reasons to the other party involved, so that he will not be offended. We ask Allaah to protect us and you from all kinds of evil. And Allaah is the Source of strength.