Horrible stink in apartment currently

The living room has a strong stench similar to rotting eggs or trash or sewage or something, and the kitchen has a similar smell but in there it smells more like sour milk in my opinion, mixed with sewage. Both rooms has had the window open all day so they are not supposed to smell and the rooms are clean too. Ive never felt this stench before in the apartment ever, and why only in two rooms and why not in the hallway between the rooms??? It makes no sense. I have a horrible headache and im getting concerned that the smell is caused by something that is affecting me this headache because its not my usual headache and I feel a bit weird but maybe im just getting sick. But any ideas what could cause this? Its truly disgusting like sitting in a room full of trash.