Female cats strange behaviour?

I have a Female cat about 3 years old, she has been neutered, but she is behaving really weird like she is in heat, miaowing, rolling round the floor, eating and eating, and he stomach feels hard and swollen to the touch, also a couple of days ago there was a bloody mucus round her backside, im quite worried and i think a trip to the vets is in order but until i can get there, does anyone have any ideas what it could be?