I 'm a girl that has a deep sense to Islam, I pray and do all what Islam ask us to do read Qur'an, do good. I'm very loved person by people (Al-Hamdu Lillah) very kind but the problem is that I did some sins as any human being I had a boy friend with whom I sympathized and other things (I never accepted to do it I told him that it is Haram but I loved him). But I was not relaxed when doing that and I keep always praying, I regret that and I want to ask God for forgiveness. The other thing that I want to wear Hijab but it is not acceptable in my job (I inform you that I need to work for my family).

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

It is mandatory upon you to make sincere repentance from these sinful relations. If you are faithful in your repentance, Allah will accept it and forgive your sins. There are many verses in the Qur'an that give good news to those who turn towards Allah in sincere repentance.
Allah Says (interpretation of meaning): {Say: "O 'Ibâdî (My slaves) who have transgressed against themselves (by committing evil deeds and sins)! Despair not of the Mercy of Allâh, verily Allâh forgives all sins. Truly, He is Oft-Forgiving, Most Merciful.} [39: 53].
The conditions of a repentance is giving up the sin, feeling deep sorrow for what was committed and taking a firm decision not to do so again.
As for Hijab, Allah ordained every pubescent Muslimah girl to wear it. So, the Hijab is actually the sign of being obedient to Allah and also in order not to expose her beauty to alien men. Allah Says (interpretation of meaning): {O Prophet! Tell your wives and your daughters and the women of the believers to draw their cloaks (veils) all over their bodies (i.e. screen themselves completely except the eyes or one eye to see the way). That will be better, that they should be known (as free respectable women) so as not to be annoyed. …} [33: 59].
Thus, leaving Hijab is not permissible at all. Know that the actual field of a woman is her house, not outside. However, if there is any necessity to go outside, she should wear complete Hijab. Therefore, we advise you to seek other work where you can abide by the rulings of Hijab. If you do not find another job, and it is compulsory on you to spend on your family then you may continue in your current job till you find another. Allah Says (interpretation of meaning): {… except under compulsion of necessity? …} [6: 119].
Allah knows best.