Implantation bleeding or no? (No picture)

Morgan

Okay, so I am not due for a period until the 23rd of this month. I started bleeding on the 13th (2 days ago) and it was very light, it only lasted for a day and a half. Today is the 15th and I am not bleeding at all. I woke up this morning feeling irritable and I had an extreme headache. I am also very emotional today. I know it's too early to test, but does anyone have any clue as to what it might be? My period usually last for 5-6 days and the bleeding is usually moderate (not too heavy and never this light). I have been very tired lately but I still don't think I am pregnant...