Ay, sobrang common yan actually, a few of us had the same experience and it could be spotting, implantation bleeding, or honestly, kahit hormonal fluctuations lang talaga, lalo na if minimal lang ang dugo. Pero since you're worried at gusto mo talagang malaman, i-suggest ko talaga na mag-check ka na with your OB para ma-confirm through ultrasound o blood test, kasi sila lang talaga ang makakasabi with certainty kung pregnant ka or what's causing it, don't wait for June 3 pa.