Pregnant or Period?

Kristen

My period is unpredictable when it comes to time. My cycles are anywhere from 27-32 days. I'm "expected" to start today. However, my periods are VERY predictable when it comes to flow. I start out of no where and it's heavy immediately. Today is different. I have been having brown spotting all day and nothing else. Could it be implantation or do you think it's my period? I tested this morning and it was negative.