Red mottled blotches on tip of penis, and small cuts on foreskin. what could this be? only one sexual partner.

Balanitis: If you are uncircumcised, probably balanitis -- i.e. inflammation of the head of the penis. Most balanitis is due to yeast, perhaps especially if your partner is female and carrying yeast in her vagina; or "nonspecific" balanitis, which often clears with increased hygiene, i.e. soap & water twice daily. See a doctor if that doesn't clear it up within a few days.