Both of us never had sex before. The first few times that a woman has intercourse, an unstretched hymen can cause pain. And whenever a woman may be tense or preoccupied, the vaginal entrance is not likely to loosen up enough and getting the penis in might hurt.
Timing is important.
Don't rush her, be patient, and work at turning her on until she is physically ready for your penis to enter. There is no clear cut answer to how long thrusting during intercourse might last. The thrusting can last anywhere from a few seconds to a few hours, with most sessions lasting somewhere in between. Using a condom reduces the sensitivity of the penis, allowing thrusting to last longer. But, remember that it's not the amount of time the man is inside the woman that counts, but the quality of the total sexual experience for both partners.