I am responding to this as a veteran of this problem. I am a veterianry technician, about 4 yrs ago I adopted Melody from the shelter as a 8 week old kitten. She was spayed at my hospital a few weeks later. For 1 year she was fine then come spring again she posessed the same signs as your kitty, very vocal and affectionate. I took her back tothe vet and explained the signs, I did not believe she was in heat again since I assisted with her spay. After taking her to a vet that I do not work for, we came to the conclusion that she must have some ovarian tissue left. We consulted a reproduction specalist and they told us that it can take as little as a few cells to cause her to go into heat. We did an exploratory surgery that I am sad to report did not go well. 2 weeks after Melody's surgery she still was not recovering well. As a tech of 6 years I was sure to keep an eye on her and I took her back to the vet and told them something had to be wrong, she was just not herself. After doing an ultrasound, we found that the surgeon had accidentally tied off her left ureatur-leading to her kidney and we had to do an emergency nephrectomy ( remove her left kidney!!). Melody came through the surgery with flying colors, but I can honestly say that I highly discourage you to go in and explore your kitty, since there can be complications. I have since then tried the stimulation approach-cats are not like us in the respect of releasing eggs to reproduce. Cats will release an egg only when stimulated (sex) so the specialist told us that we may be able to stop the heat cycles by sexually stimulating her. I have to say it was not exactly something that one should have to do to their kitty, but with the vets assistance we "helped her out" and she has not gone into heat for 2 years now. You may want to talk with your vet and see if this is an option for you-it sure beats surgery looking back now!!! Please let me know if there is anything else I can do to help.