If your normal cycle is appx 24 days, as your question suggests, then I'd say that it's highly possible that you're in the "puddin' club"! (as anything from 21-35 days+ is a normal cycle, with average being about 28)
This is assuming that you haven't just finished any kind of hormonal birth control method, that can leave your cycle a bit topsy-turvy for a few months til it settles down again.
Your symptoms would certainly fit either scenario, so only you know what's premenstrually normal for you.
I did tests, with both of my pregnancies, the day after my period was due and they were positlve, so get yourself down to Boots girl!
Please keep us posted.
Minz