All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Marrying such an orphan, who had lost her parents and who is in a real awful and critical situation is a praiseworthy deed and we ask Allaah The Exalted to generously Reward you for it. Moreover, bear in mind, dear questioner, that the command of the Prophet, sallallaahu ‘alayhi wa sallam, to marry affectionate and fertile women is for exhortation and guidance to what is of best interest and not an obligation.
Furthermore, bear in mind that infertility problems for both women and men are not decisive or final; as many sterile spouses had children after a very long waiting period. However, if Allaah The Exalted Did not Bestow the blessing of children upon you, you may take another wife while maintaining your first marriage; for Allaah The Exalted Permits polygamy for the Muslim man as long as he is able to shoulder such a responsibility without violating or neglecting its due rights and responsibilities. Allaah The Exalted Says (what means): {Then marry those that please you of [other] women, two or three or four. But if you fear that you will not be just, then [marry only] one or those (whom) your right hand possesses.} [Quran 4:3]
Allaah Knows best.