Knowing our sins is a grace from God. As we grow more and more intent on imitating Jesus in every aspect of our life, to love only what He loves, to forgive, to be generous, to be compassionate, especially to the poor and those most in need of God, we would more and more be able to see clearly our own selfishness, worldliness, miserliness, pride, greed, lust, envy etc. It is for this reason that it is not the beginners who tend to go to confession frequently, but those who are seriously growing in depth in their walk with the Lord, since the closer they are imitating christ, the more they can see clearly their flaws.
Since it is a grace, you must slowly yield to it. One does not just start going to confession weekly if there is really nothing to confess. One should instead develop a habit to examine his own conscience every night. I suggest that in your case that you use an examination of conscience booklet. Many churches have such booklets available. Today you can also find some really good ones online as well as phone apps.
These tools usually go through the Ten Commandments and the seven deadly sins to list out the wrongs you might have committed. But the really good ones also help you to identify the good deeds that you might have failed to do. Knowing what I have done wrong is only half the list. The other half is whether or not I have squandered the opportunities God has placed before me to be charitable to others. For example, I have seen one going through the 7 virtues to help the penitent reflect if he has tried his best to grow in them in specific situations.
As to your example, venting itself is not a sin, if you have put the focus on how you feel and not who so and so has done, if you have done your utmost diligence not to provide information so that the honour of the individuals may be protected. Otherwise, you run the risk of venting in name, but gossiping and caricaturizing in fact, and that is a serious offence.