Dark Brown Discharge

Ok so I am 16 and have not started my period yet. I have had pretty heavy, clear-whitish discharge for several years now. Just a few days ago something weird started to happen. My discharge is dark brown/blackish and spotty. It's still really thick and there's a lot of it. I haven't been getting cramps. My skin is fine (for once). My hair is pretty oily even though I just washed it. And for the first time in forever I don't have a headache. I am, however, exhausted. The reason I'm telling you all this is because everyone says I'm probably getting my period, but that just doesn't seem right. Any ideas?