I am a 32 year old male. When I have sex with my partner, I ejaculate in from 7 to 15 minutes on first time. When we tried for the second, I can't ejaculate even if we have intercourse about or more than half an hour. I got exhausted in this process. We stop start for some time but the result does not change. I don't lose erection but no ejaculation and orgasm climax attained. What could be the reason? Should I consult to a doctor?