I've had spotting on the 21st and the 26th of march but no regular menses. 17 days late and negative hpt last week. what's wrong with my body?

Likely nothing wrong: Menstrual irregularities are not uncommon. A common cause is anovulatory cycles. See this site for more info. http://www.nichd.nih.gov/health/topics/menstruation/conditioninfo/pages/causes.aspx.

May not have: Ovulated this month causing the symptoms.See what happens over the next month or 2. If this continues over the next couple of months see gyn.