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.
We congratulate you on the favour of Islam that Allaah has bestowed on you, and we ask Him to make you firm on the truth until the day you meet Him.
If the case is as you mentioned that the first marriage was an Islamic one taking place with the permission of the guardian and the presence of two witnesses, you have become a wife to that man, knowing that if the Muslim woman does not have a guardian from among her family, the judge or his deputy can conclude her marriage. For further information, see Fataawa 88488 and 83629. So, if you are a wife to that man, the second marriage will be invalid.
Supposing that you married the first man without a guardian or the presence of witnesses, marriage would be invalid according to the preponderant opinion of scholars. Yet, it is a doubtful marriage, so it is not permissible for the woman to remarry until her first marriage is nullified or divorce takes place. For further information, see Fatwa 92478.
Since the second marriage took place before the nullification of the first marriage or divorce, it would be invalid as well and you must leave the second husband. If the second husband consummated his marriage with you, you have to wait for three menstrual periods until you find out that your womb is free from pregnancy or until you give birth if you are pregnant. The child will be traced back to him if he considered his marriage to you as valid.
On the other hand, if the first husband is proven to have divorced you, it will be permissible for you to marry another man, but this must be after establishing that you are not pregnant as we mentioned before. You should contact those who are in charge of the most trustworthy Islamic centers in your area and submit your case with this Fatwa to them and you will find the appropriate solution – Allaah Willing.
Allaah Knows best.