Abnormal period or implantation bleeding?

Abnormal period or implantation bleeding, how do you tell the difference? Ok so here is my sistuation, I'm sexually active with my boyfriend, we are very careful, I'm on the pill which I take religiously every day at the same time. My period is very regular and has been the same for years. But this month it's completely different, day one, which was three days ago, was extermly light bleeding and bright red. Barely needed one tampon had to switch to a pad it was so light, when regularly its very heavy bleeding and dark red almost brown, typically I bleed throught five or six super tampons on day one. So I was a little concerned, wasn't sure what to think. The second day was very light more like spotting and day three, being today, has pretty much been nothing tell the evening with light spotting but really dark almost black. Over the past few days cramps have come and gone I've also been feeling nausea. Because its so close to the holiday I'm not able to see my doctor for a few more days, so if anyone has been throught anything similar or has an option or advice it would be greatly appreciated.