Don't panic...
As mentioned in the replies so far, did any upsetting event take
place lately? Have you been getting enough sleep? Are you stressed?
Or do you have too much free time on your hands and too little to
do?
Sometimes we don't remember things because er, something like, when
they are presented to us, we put it on low priority so we tend to
not remember them. For a start, maybe you can try (I know this
sounds stupid but it kinda worked for me a bit) reminding yourself
to give more importance to certain things so you'll remember them
better...
If you have too many errands on hand, it helps to make a list of
them, crossing each out upon completion. A list is not only a way
of making sure you don't leave out things you need to do, it also
helps to lighten the burden on your brain by freeing up some space
for other details to be remembered...
Just try to be a bit more organized loh. 
