It is likely that something got into the can between the liner and the can itself. You may have had an unnoticed leak in a recent bag of trash. When that dreaded event happens (it happens to everyone on occasion) it usually leaves a clear unnoticeable liquid... unnoticeable until it starts to stink.
I would start by emptying the current bag of trash and taking the can outside. Put some dish soap in the bottom first, then spray with a spray nozzle on the garden hose, until it sudses up some, and (using rubber gloves, b/c, well, ick!) scrub inside the can, especially the flat bottom. Spray rinse. Let it sit in the sun for an hour or so. Then bring it back in and either wipe it down with vinegar (inside of it) or spray it with a Lysol kitchen spray, let it sit for a minute or two and wipe it clean. THEN, let it completely air dry, before putting a new bag in it.
That should solve the problem, if you have odors in the can itself. It may also be that you have thrown in more pungent items recently that spoil more quickly, particularly if your home is hotter inside than normal right now.
Any kind of meat (cooked or uncooked) will reek in a short number of hours. As will any sort of melon rind (watermelon, cantalope, etc).. veggie peels aren't usually a problem. But melon rinds can take your breath away after just overnight.
Good luck.