Welcome to HCM.
Don,t worry, nothing serious.
It must be due to some sexual injuries
that had happened during your first coitus which had not completely healed. Further intercourse with unhealed wound will result in bleeding every time. It may be too tiny and you wouldn't have noticed at all.You have to take some drugs to heal the injury
from your physician or Gynecologist and abstain totally from sex for at least a week or two. The you will be alright and you will not bleed further during sex.
Wish you a speedy recovery.