@mummymaybe: I had late onset OHSS when I got my BFP (nearly fell off the bed in emergency when they told me. Last thing I was expecting to hear).
Anyhoo..yes..look out for the signs..mine were severe bloating, headaches, excessive thirst, nausea, urine got darker like apple juice @ output slowly got less @ less especially in relation to the amount I was drinking @ stomach pain...why OHSS never even entered my mind at the time I do not know??
I upped my protein intake, got stuck into the sports drinks @ Sustagen too. Some kind of heatpacks on standby @ some decent painkillers on hand would also be a good idea. Wazza will prob give you a script for something if you ask.
Good Luck Luv!!! Hope you'll be ok...