My Last Period Ended On 3-16-16 And Started 3-12-16. I

My last period ended on 3-16-16 and started 3-12-16. I was sexually active with my boyfriend on 3-27-16 and noticed some pink spotting on 4-2-16 and nothing but once that day and not expecting to get my period until the 4-7-16 or 4-8-16. Is this a sign of implantation and how to use a ovulation calculator ( do you use the first day you start or the last day of your period) I'm confused