You are describing new onset of short-term memory loss. Your brain stores new information on a very temporary basis. Then, your brain must process this information. Otherwise it will be lost. If youre not concentrating on new information or become distracted as you get new information, even a young person like yourself can forget information similar to what you describe.
But you said this has happened repeatedly. So you should see your doctor for an evaluation.
There are multiple possibilities for new onset short-term memory loss. One of the more common ones is emotional stress. This is even more likely if you have anxiety or depression.
Other causes include:
- Head trauma with a concussion<.li>
- A severe medical illness
- High fever
- Over-use of alcohol or drugs
- Some medications
At your young age, I am less worried about some underlying brain disorder, such as Alzheimers or other dementia. But you should see your doctor to discuss your symptoms.