Implant

Okay so, I've been on the contraceptive bar for four years now (had it reinserted after the third year, like you're supposed to) but my periods are still all over the place. I could get a really mild period for two months, then nothing at all for six months etc... I'm lucky I've never suffered from heavy periods but at the moment I'm another week late for my period and it's starting to annoy me. I feel like this can't be good for my body to be so irregular? Opinions please ladies! :(