Some habitual sin is so ingrained in our personality that it is difficult to overcome. This can be due to psychological wounds we received as a child, patterns instilled into us by relations with our significant others (parents, siblings), or whatever. For example my wife was brought up in a hyper-critical family. Nothing was ever right, and the thing about her that drives me nuts is her inability to freely accept something done for her out of love, without attaching a criticism to it (“thanks for doing the laundry, but next time could you fold it this way…”).
Unfortunately some of the patterns are very bad, for example sexual, physical or emotional abuse as a child can lead to some very serious problems as adults including sexual sin.
Are these mortal sins? I rather doubt it. For example if you habitually lie because as a child you needed to do it to spare yourself a beating, I doubt habitual lying as an adult is a mortal sin. But if you didn’t have that issue as a child, and tell a whopper now to say, avoid paying too much tax or being caught with your pants down, that is probably mortal.
So for those things ingrained in you, you need to go back to the source, identify the reasons, forgive yourself (and if you can, those who harmed you), and then with the help of a confessor try to break the pattern. It won’t be easy and you will repeatedly fail, but you don’t need to beat yourself up and go to confession every single week over the same thing, but you should probably still avail yourself of the sacrament.