Few months ago i did a major sin. I repent and i seek forgiveness to Allah every day. But it chase me in my sleep. I can't even moving on. Getting weak day by day. What should i do?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

You have indeed done well in your repentance and seeking forgiveness, this is the most effective treatment for those who fell into sin. You should trust the promise of Allah in accepting the repentance of His Servants if they repent and ask for forgiveness. Allah Says (what means): {And those who, when they commit an immorality or wrong themselves [by transgression], remember Allah and seek forgiveness for their sins - and who can forgive sins except Allah? - and [who] do not persist in what they have done while they know. Those - their reward is forgiveness from their Lord and gardens beneath which rivers flow [in Paradise], wherein they will abide eternally; and excellent is the reward of the [righteous] workers.} [Quran 3:135-136]

Allah also Says (what means): {And it is He who accepts repentance from his servants and pardons misdeeds, and He knows what you do.} [Quran 42:25]

Allah further Says (what means): {And whoever does a wrong or wrongs himself but then seeks forgiveness of Allah will find Allah Forgiving and Merciful.} [Quran 4:110]

Another verse reads (what means): {But whoever repents after his wrongdoing and reforms, indeed, Allah will turn to him in forgiveness. Indeed, Allah is Forgiving and Merciful.} [Quran 5:39]

Besides, the Prophet said: “Allah, the Exalted, said: 'O son of Adam, so long as you call upon Me and ask of Me, I shall forgive you for what you have done, and I shall not mind. O son of Adam, were your sins to reach the clouds of the sky and were you then to ask forgiveness of Me, I shall forgive you. O son of Adam, were you to come to Me with sins nearly as great as the earth and were you then to meet Me, ascribing no partner to Me, I shall bring you forgiveness nearly as great as it.” [At-Tirmidhi who graded it as Hasan, and al-Albani classified it as authentic]

Also, it is confirmed that the Prophet said: “The repentant of sin is like one who has never committed a sin.” [Ibn Majah and others]

The Hadith reported by At-Tirmidhi reads: “Allah, Blessed and Exalted, accepts the slave's repentance as long as his death rattle has not yet reached his throat.”
As-Sa’di said in his Tafseer (interpretation of the Quran):

{And those who, when they commit an immorality or wrong themselves [by transgression]}, i.e., they had committed great bad deeds, or something less, and they took the initiative to repent and seek forgiveness, and remember their Lord, and what He threatened the disobedient people with and promised by the pious people with, so they asked Him forgiveness for their sins and covering up their sins, while quitting them and regretting them, for this He said: {and [who] do not persist in what they have done while they know. Those – who have these qualities – their reward is forgiveness from their Lord – (a forgiveness) that will remove all which they fear (of punishment) – and gardens beneath which rivers flow [in Paradise] …” [End of quote]

As for what you see in your dreams, there is no consideration for it, as the sleeper is not blamed for what he sees in his sleep.

So, observe the Adhkar (i.e., remembrances that are said) when going to sleep and beware of despairing from Allah's Mercy and His acceptance of the repentance of His Servants. You should be keen on performing acts of obedience and good deeds and staying away from what reminds you of sin, such as thinking about it and keeping company with bad companions.

Allah knows best.