A bad mouth smell is often detectable by everyone but us. 1. Lick the back of your hand and wait 15-20 seconds for the saliva to dry. Now, all saliva has some kind of odor, however, if the smell is particularly bad then most likely you have bad breath (you'll see how to fix it shortly).
Check it carefully to see if it's white (particularly in the back or base). If it is, then that's a sign that you could have bad breath. A dry mouth is more likely to smell but that can easily be solved with a tall glass of water.
Now even if your tests come out positive, don't despair. There are many ways to get rid of bad breath: some temporary and some permanent.