Cat in heat?

I tried reading some old posts about this but couldn't find anything definative. My cat is about a year old and she has started acting very weird. She follows me around like crazy, meows quite a bit and is licking stuff a lot more. Is this heat, it kind of sounds like it but I'm just making sure.
Now she's spayed so she definately isn't pregnant but she her lower stomach near her ovaries seems very big. For awhile we just thought she was fat but it seems bigger than normal, could it be a tumor or something? I know it's hard to say but any info would be great thanks!
Julianne

This kitty needs to go to the Vet, ASAP! She is in pain, and is telling you that with her meowing and licking. Also if her abdomen is swollen that too should tell you that she needs your help. Please take her to the Vet, a spayed cat does not come into heat.

Well ok, she still seems happy but I have a vet appointment set up so thanks for the advice!