I noticed a bad smell in my kitchen, what could it be?

Today my kitchen has been smelling progressively worse near the dirty dishes, our sink, the fan, the oven, the compost container (closed), and heater. I can't figure out where the smell is coming from, or what is causing it. It's a sort of rotting smell, a bit like rotten fruit, and it might be making me lightheaded (can't tell b/c I think I might be getting a fever...). My brother describes it as "rotting poop", and it smells like it could be the compost, but I just want to check that there isn't anything serious it could be. Thanks!