If you feel as if you have sinned when it comes to sex or lust, don't have any fear in that confession, regardless if it wasn't venial or not. A priest will still help you understand the morality and your responsibility in these matters. When it comes to other issues, only confess those sins that are mortal, not venial. For example, if someone says something to you and you have feelings of hate to that person. That's not a sin, that's human nature. If you punch him in the face, attack him, or scream back at him, then that should be confessed as a sin. There is nothing sinful about human emotions. We all have them, it's how we act on those emotions is what makes it immoral. I would ask your parish priest about it. This is one thing I wish more people would do. The sacrament of Reconciliation is a sacrament and should be practiced regularly but it ends up getting tossed to the side by most Catholics.