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.

Vinegar...I know at first  we all thought 'Yeck'  Just try it. White vinegar is an amazing tool for so many cleaning jobs around the house. Don't worry about the smell. Within minutes  it dissipates,  neutralizing the bad odor with it. It is one of the oldest cleaners known to mankind.  Chopping onions or seafood, afterward rinse the area and your hands with a combination of vinegar and water. If you have cut any kind of meats,chicken  fish etc on a cutting board,first warm soapy water for plastic boards.  Then  rinse the board, counters & sink surfaces with Vinegar/H2O. When we had  Ceramic Tile put in the kitchen floor the salesman told me to use 'just vinegar and water', never soap or detergents too slippery!    My Mom always cleaned her windows using Vinegar/water...No streaks left behind.

      It  also softens your skin incredibly, while your at it. Summer time feet sweat, actually our bodies all over. You can soak your feet in warm water with some vinegar added. Many old timers added it to their bath. Besides helping cleanse and freshen the body it will soften your skin all over. One of the best ways to take the sting out of a sunburn is to add vinegar (maybe about a cup or more) to your bath. It will soften and calm the burnt/irritated skin.  Google it, there are probably 100 diff ways to clean and neutralize odors  for way less money than store bought cleansers. It is  most economical to to buy a gallon and keep it under your sink. Diluted with plain water in a spray bottle 50/50 for heavy duty cleaning.  I almost forgot, throw a cup in with any laundry that has been sitting in the heat. We could go on all day. It truly is the oldest & most inexpensive cleaner.

It might be a dead mouse in the wall or one of the air ducts. That happened to us when I was a kid growing up. We thought it was the drain, the trash,etc. Then finally, the smell got so bad we were able to pinpoint it. A dead mouse under the dishwasher.