Sounds like a missed miscarriage. It's where the baby stops development, but your body doesn't recognize that it's happened and doesn't expel the tissue. It might happen in a few weeks/days, or you'll have to go in for a d&c.
I agree with Clysta. Sometimes your body doesn't realize it isn't viable which is called a missed miscarriage. When that happens they can give you a medication or do a D&C depending. Hopefully if it is a miscarriage your body will realize it and things will naturally take it's course. I'm so sorry