H.V.
I've had Paraguard in since last October. No side effects except the heavy period thing. Which is normal.
My cycle does the same thing you are talking about.
Every few months or so I would get this issue too.
I would know that my period was supposed to hit on , lets say the 13th, By the 17th..nothing. Some cramping, that lil bit of brown that you are talking about too.
Then I would get a FULL on period.
I was scared shitless that I was pregant.
It IS possible, but very rare. Most of the time they do end up in miscarriage. Or they can be even more dangerous, most can be ectopic pregnancies.
I would say, if you are really worried, take a test.