My cat hasn't been in heat since giving birth in July?

So in late July, my small cat gave birth to two kittens who were unfortunately stillborn. Since then, she hasn't been in heat. I've read that it can take a couple of weeks, but it's been quite some time now. A few weeks after giving birth, she started "calling" but it was nothing like it was before when she would go into heat, it was very minimal and didn't last all day. She also hasn't been marking her territory like she used to (which i'm not complaining about, cause she used to pee all over the couch and bed.) I'm just curious if there may be something seriously wrong with her or if it's nothing to worry about.