Ecigarettes are not harmless and neither is their vapor. They have not been around long enough for anyone to even verify that they are better for you than cigarettes, but studies have shown that they constrict the lungs and airways and sometimes the vapor can be irritating to your throat and lungs. If you're using the cartridges with nicotine, your body is not really detoxing from anything but the crap thats accumulated in your lungs and you're still at increased risk for strokes, heart problems, premature aging, tooth decay etc, as these are side effects of nicotine (its not a harmless substance).
It IS normal for your lungs to clear themselves after you quit though. You might find you are coughing way more and hacking up a lot of stuff--and it can take months to get it all out for some people.