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 is His slave and Messenger.
First of all, you should know that repentance of your sin is not attained by merely getting married; rather, you should fulfill all the due conditions of repentance as underlined in fatwa 83629. However, that the repentant abstains from committing the unlawful and hastens to get married indicates that the due conditions of repentance are mostly fulfilled.
Undoubtedly, your child is attributed to your husband because he was born after six months of marriage; please refer to fatwa 122443.
Muslim jurists held different scholarly views regarding the ruling on the marriage of an adulterous couple before repentance and before confirming that the woman is not pregnant; please refer to fatwa 83176. Hence, your marriage is valid based on the scholarly view suggesting the validity of such a marriage. You should also know that the person suffering from waswaas (obsessive whispering) is entitled to follow the easiest and less stringent scholarly view in case of matters open for scholarly difference of opinion so as to avoid any hardship or difficulty incurred by such waswaas, as highlighted in fatwa 140014.
Based on that, you should resume your life with your husband as if nothing had happened and not allow Satan to disturb your life and cause you distress by means of such waswaas.
Allaah knows best.