You cannot be sterile as you conceived twice. The position of the uterus
being backward or retroverted, is not a major concern, and can be managed with certain precautions. This position can pose a problem in conception as the sperms have a difficult route to follow. Therefore, you should lie on your belly for about half-an-hour after intercourse to facilitate easy ascent of the sperms. Apart from this, you should get properly investigated by a specialist to look for other causes like hormonal
insufficiency or tubal blocks and get further management. Hope this helps.