I used to pray without wearing Hijab (veil), as I did not know of its obligation during prayer.
Should I repeat all the obligatory and supererogatory Salahs even though this has been happening for almost six years?
If you were truly ignorant of what should be covered while praying, you do not have to repeat Salah for the past period. You should repent to Allah and increase doing righteous deeds for Allah (Exalted be He) (Part No. 6; Page No. 176) says,
And verily, I am indeed forgiving to him who repents, believes (in My Oneness, and associates none in worship with Me) and does righteous good deeds, and then remains constant in doing them, (till his death).
There are also other Ayahs that relate the same meaning. It is worth mentioning that it is permissible for a woman to uncover her face while praying unless she is in the presence of Ajanib (men other than a husband or permanently unmarriageable male relatives).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.