Have good sleep, do exercise & yoga daily for 1 hour. Take hot milk 1 glass morning & evening. Avoid spicy. Chilli.nd fried food Take CP SHILAJIT tb. Manmath ras. Nd tb. Sidh makardhwaj bati. One each morning & evening for 3 months. Wd hot milk. See d results or otherwise consult a sexologist personally.

You getting erection in foreplay followed by vaginal penetration and able to sustain for sometime in intercourse indicates normal erection mechanism. Loosing erection even with slight inturruption for few seconds may be due your diversion of mind. It appears apparently you are maintaining your penile erection only by mere mechanical friction and not with full romantic and passionate mind. You should understand that sex happens well when bodily and psychologically you are involved in the act. However, some test like Penile doppler test with Prostaglandins dose and sex hormone estimation are required too.