Ay, I've heard about this from a few of my mum friends with implants, spotting kahit after a year is actually pretty common since implants can mess with your hormones pa rin, pero 4 days straight and recurring like that is worth checking with your OB to be sure, lalo na if it's heavier than usual spotting. One of my officemates had something similar at first kaya nicheck lang niya, and turned out it was just adjustment, but better safe than sorry talaga especially pag ongoing na.