Bad smell in the house makes a person sick to the ...

Maybe your neighbor murdered someone?

I dunno. Have you checked for dead animals? Like rats? Maybe you are a neat person, but I remember when I was living with my dad. He was a neat person, and he constantly sprayed me down with Lysol--he did it a lot more when I was sick, though--but then he found a dead rat in his wall. It was nasty.

It could be anything, though.

it might sound odd,  but buy some lemons,  and oranges, peel and thinnly slice add to a  sauce pan ( size the pan depending on how many you are going to use). Simmer untill the juices are begining to get warm. Squeeze the rest of the fruit in to the pan and add a TINY  bit of organic sent free dish soap. straing with a paper towel or coffee filter. then clean all the surfaces in your home. In cluding the trash can and floors. Dont use on wood floors or carpet. The citrus from the fruit will get rid of the foul smell and the soap will get rid of any bacteria. if you have a garbage disposal cut a grapefruit in to quarters, and one at a time run each peice through, dont use ant water for about fifteen mins after the grapefruit. i have done this so many times, your home will smell great. (you can also use this as an air freshener, just take out the dish soap)

Tori, did you just notice this smell or has it been there for a long time?  Could it be a musty smell from somewhere?  Or a sewer smell coming out of one of your drains?  Is it all over the house, or does it just seem to be coming from one room.  If you can't tell, try keeping the doors to each room closed all night and walking into each, sniffing to see if the odor is stronger one room than another. 

A friend of mine got divorced years ago and was awarded their house.  She started noticing a smell and couldn't figure it out, but it seemed to get worse and worse.  A group of friends all went over and started our sniffing--could you imagine our surprise when we found shrimp in her floor heating ducts?  And, not just a few, the sucker must have spent a fortune buying them.  Needless to say, she got even.

If you tried everything and failed, get a Hepa Air Cleaner. They are a blessing.

Draino in the drains works wonders on unknown oders.  Even just good old vinegar poured straight into drain & allowed to sit for awhile will do the trick. 

Could be from past renters, try painting and replace carpets.