This is actually a working memory issue, rather than short term memory.
Info comes in and you're supposed to hold it in this working memory cache wheilst you decide what to do with it, how to use it.
Some bits are discarded, others are transferred to short term memory. In turn, items that are repeated, that you concentrate on, that are brought to your notice though their attachment to high emotional importance are transferred finally to long term memory.
That's basically how it was explianed to me by the psychologist who tested my memory functions. Think of a pc with HD (long term memory), cache (short term),
What happens is the program and data is loaded from the hard drive into RAM (short term) and then into cache RAM (working) where the info is operated on (using CPU) in the moment. Or vice versa.
And yes, my working memory is rubbish - as Paul descri bes. I am completely wedded to my laptop - it is my working and short term memory. Without it I would be living in a complete haze of info that i find very difficult to sort out. Indeed , before computers I lived the whole of my life in a fog.
The ironic but typically aspie adjunct to all this is that I have the amazing hyperfocus and ability to work with very specific data for extended periods of time. Computers have extended my capacity wonderfully.