My penis has raw skin under the head & it bleeds after sex?

Frenulum... Without picture, i guess the structure that you tried to describe or refer is anatomically called frenulum praepulii penis, which is just like the frenulum of tongue and ease to bleed if being tight and stretched. Sexually, it's a sensitive spot for arousal similar to the corona of penis usually, it's not an issue of concern. For detail, go to check with urologist.