My cat has been spayed 6 months ago, and I took her to the vet as she is acting like she is in heat. The vet says no she is not, but may have a harmonal imbalance. The vet said she would research it and get back with me in a week, but this cat is driving me bonkers with all the "talking" and undulating around she is doing. Has anyone else had this problem. We found the incision where she was spayed, so I know that it was done..

I have heard of instances were cats are spayed, but the vet fails to remove the entirety of the uterus, leaving a "stump". This can cause signs of heat. The only way I know of to cure it is to remove the remainder of the uterus.
You'd need an ultrasound or MRI to diagnose it, most likely.