I have no stress, exercise has not changed, maintained weight

So normally I get cramps before I start but two days ago I started what was an unusually light period It's not a constant flow it's only here and there. I only had light cramping on first day. I normally have really bad cramping, food cravings, heavy bleeding, and mood swings, and with this it's like not even a period it's so insignificant. I have no stress, exercise has not changed, maintained weight, only thing that has changed in last two weeks is my diet a little. Today is third day I have seen no bleeding so far I have no other pregnancy sym just headaches IM not supposed to start til next week. I am 25 and sexually active with my husband. By the way tmi but blood in beginning was brown then changed to mixture of brown and red almost pink color. I took a Oregon test this morning says negative. Any ideas