What Causes Vaginal Bleeding After Intercourse?

I am 50 years old and I had intercourse yesterday. I am menopausal. My partner is rather large and I bled during penetration. Bright red drops. It stopped pretty quickly. I think I was aroused enough to be sufficiently lubricated upon initial penetration...could I have become dry and his penis irritated my vaginal walls or could his hitting my cervix repeatedly cause the bleed?