feeling v nauseous - not pregnant

[icancancan]

wonder if anyone can shed some light? I have had bouts of nausea off and on for the past few months. GP has given me stool sample thingy and has asked me to provide a sample if possible during nauseous period - which usually seems to be the weekend so no sample yet provided (as needs to be 'fresh' - sorry if tmi!).
This week I have felt crap - sudden vomiting all night on one night (no runs though) and have been feeling weak and nauseous since. I'm drinking lots of fluids with rehydration sachets and have begun to eat plain foods but still feeling crap.
Its very debilitating as I can barely get up, but still need to work, pick up ds, cook etc although dh doing what he can.
do you think I could have a norovirus? does this stay in the system and recur?
any experiences welcome

Appendicitis?

thanks bbh - had not considered that as thought you usually experience severe pains - I'm not in pain as such, just sick.

Not sure but when I get pmt I get nauseous and vomit [have ended up in hospital] and diarrhoea
I also get reflux and stomach pains it generally lasts 7 - 10 days some days I cannot even manage water. It took me months for it to click.
It could be stomach bug apparently it can last a few weeks [not the bug but the side effects]
Have you eaten anything specific prior to being ill? have you tried to keep a diary describing how you feel and every thing you eat and any meds you take. If it is not a bug and they want to check for allergies/intolerance you have half the job done by keeping a diary.
Hope you feel better soon