Hi the bible says that we should not sin, we should be living trying to avoid sin, but if we do mess-up Jesus will forgive us.
1Jn 2:1 My little children, these things write I unto you, that ye sinnot. And if any man sin, we have an advocate with the Father, Jesus Christ the righteous:
1Jn 1:9 If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness.
What you are experiencing is an attempt by Satan to unsettle your faith. He wants you to think you have committed an unpardonable sin so you get angry with God, and leave your faith behind.
In reality there is no sin that is unpardonable, blasphemy of the Holy Spirit is pushing away God's love and drawing to salvation for so long that we become hardened and no longer responsive to God. Sin has a hardening effect, Paul describes it in terms of slavery:
Rom 6:15-16 What then? shall we sin, because we are not under the law, but under grace? God forbid. Know ye not, that to whom ye yield yourselves servants to obey, his servants ye are to whom ye obey; whether of sin unto death, or of obedience unto righteousness?
If we continually sin our hearts become enslaved to it, Satan becomes our master, and we start to get blinded spiritually, persistent sin leads to death (hell). It is a slow blinding effect, the more we sin the blinder we become to God's forgiveness. The unpardonable sin is persisting in sin for so long we can no longer see God's grace.
Also in regard to the attacks on your mind. Forcefully remind Satan that in Christ:
Gal 3:13-14 Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree: That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.
What that scripture means is that because Christ is in you, because you are a Christian, every curse that Satan tries to put on you for your weaknesses is broken. No curse can rest on you, only God's blessing.
Now Satan will not give up easy he will attack you often, but every time tell him "You are a curse, because I am in Christ, the bible says I have no curse, you have no part of me, I will only have God's blessing in my life:.