Your bathtub is over flowing into the closet of your bedroom. Make sure your shower curtain is properly drawn, and water is not over flowing when you are soaking. Check the closets for moisture.
Do you have showers or sinks that do not get used or a laundry tub or spare bathroom or a floor drain. Each of these drains has a water plug, called a P trap. It allows water down and keeps the sewer smell down, until the trap dries up and they do allow water to evaporate. So run around your unit and put 1 cup of water down the drain. That will plug it up. Now spritz white vinegar into the air in the stinky room and wait an hour for the vinegar to dry. As vinegar dries it absorbs 7 times its weight in odors. Which is handy to know when it is winter and -40F outside. Nope, not gonna air out the house until summer.
Possible water leak????
Check the drip-pan on your AC unit, if the water does not drain and sits too long....it can get really stinky/musty.
Has it rained recently? If you have a roof leak, it may be water is getting into the attic above your apartment, creating a strong musty smell. You can spot leaks by accessing the attic and looking for signs of dark and moldy insulation.
Is it humid where you live? My basement gets musty in the summer when it is humid. I set out a few containers of DampRid and the smell is gone in a day.
All of a sudden the last couple of weeks there has been a strong smell in my apartment no matter how much air freshener I use and how much I open the windows. And now suddenly this evening I have noticed some bugs in my place which never happen.
What is going on? Any idea's or suggestions? My apartment is next to the storage room if that helps at all?