Abnormal Bleeding

About a week and half ago I had some really light almost pink bleeding that lasted for only a day (possibly implantation bleeding, I'm not sure). Today I started feeling a little weird and I had darker brown blood in my underwear (which generally means it's older blood). And I don't really know what to think. This doesn't feel like my period and this isn't normal for me. Has anyone else experience this? What was going on? Any advice?