It hurts when I have sex, when my boyfriend penetrates me. Possibilities?

Vaginal pain. Partially intact hymen vs interstitial cystitis vs large male partner vs vaginal atresia. Should be evaluated by a gynecologist.
Painful sex. Painful sex on penetration deserves full gyn exam-there are many conditions which contribute to this condition. Organic defects-like narrow introitus or opening, vaginismus or spasm of the pelvic floor muscles on attempt at penetration, atrophy of vagina, lichen sclerosus -a skin condition which affects vulva and causes narrowing and contraction of the skin around vagina, infections like yeast, hpv.