You asked a question that many people think but don’t want to know the answer. I’m very happy to hear that you are seeking help. Other Catholics will also help to explain this after me since I’m not a professional.
Here’s what I would like to point out first: before mass begins, ask a priest to hear your confession so that you can receive communion. He will do one of two things. He will either hear your confession with the time left before mass or ,if there’s not enough time left, he will ask you to refrain from communion during mass, have confession after the mass, and then he will allow you to receive communion right after that on your own.
It’s so important to have a clean conscious, free of sins, before receiving our Lord. It’s great to hear how much you are trying to make sure this is done right away. Keep up the good work and keep practicing your faith to help keep anything sinful away. God bless you!