Is it a sewer smell? If so, your toilet could have a bad/worn wax ring and is letting in sewer gases.

When we bought our house the master bathroom smelled like someone had just colored their hair, with strong salon chemicals. It was a bad wax ring on the toilet letting in sewer gases.

Check behind the beds, nightstands. If you have children go on your knees and look at the floor to see what is in the area. Could be a piece of food that was dropped at some point. It could also be a house mouse that may have died recently. I would also check the shower drain and sink drain. Sometimes they give off smells similar to what you are describing.

We had that bad smell in the house we bought and couldn’t figure it out, then we ripped out the drywall around the sewer pipe and there was a dripping leak everything the toilet was flushed we had that smell.
Another smell was in one of the closets, turns out we ripped the entire wall out and there had been an entire wall full of mice.
Now we don’t have any smells. SoI would try and pin point where the smell is worst and then start looking into the walls, or pipes but first do your wax ring check as per the previous mention.

Also faucet on tub; our faucet was installed improperly and was bent behind the wall which allowed some odors......we thought it was the tub drain, but it was the faucet.