Christians struggle with sin often–every day.  Different Christians have different struggles.  The key word is struggle.  If you can sin and not struggle with it, meaning that it doesn’t bother you to sin, then you must examine your relationship with Jesus Christ.  If someone as great as the Holy Spirit comes to live within you, He will convict you of sin.  If there is no conviction, there is great reason to think that the Holy Spirit is not living on the inside–and that you do not have a genuine relationship with God through Jesus Christ.