Hi gymbunny
What kind of organisation are you in - a private company, local govt? How well this is dealt with can depend on this, as public organisations have a 'rules book' that they are kept to by the unions. Which brings in the second point, are you in a union, if not get yourself into Unison or similar very quickly. You can literally go down their office and join on the spot. You are being accused of something very serious and need a big buddy to help you. All organisations find it easier to blame the victim if they suspect you will roll over without a fight.
Don't blow up. Write down a timeline of everything that has happened with regards to the office tramp. Show this timeline to your union rep and ask for their advice. Make sure yoou discuss any correspondence or meetings with your managers in advance with your union and be very wary of any last minute calls for 'a quick chat'.
If you are being made to feel ill that is extremely relevant and you should make an appointmant to see your doctor and discuss this asap. This should also be talked thru with your union rep.
Be realistic about the organisation you work for, as even if you win they can be remarkably childish and unforgiving - are they worth the candle in the longer term - start looking now at alternative work to go to when you're ready. These things can rumble on for years. The difference is usually not immediate, but keep your end up and in a year, two years, you look back and it's often the case that things work out well, but it can seem lousy in the short term and you should brace yourself for that.
Hang on in there and best of luck.