When I was younger, I did not determine what I wanted to do for a career until I was in my last year of graduate school. When I had a chance to talk to someone in my current profession, and observe him while he was working, I knew right then that is what I wanted to be.
Interestingly, I went through high school, undergraduate studies, and most of graduate studies, without knowing what I wanted to do. I got to my current career, without losing any time, or making any wrong turns.
Along the way, I could only discern “the next step”, such as “keep grades up”, try a summer job in a certain field etc. Just “following the next step” was all I could see along the way. I attribute my ability to “see the next step”, to staying in church / staying connected to God although it did not occur to me at the time that I was being guided.
So I would say to just keep going to Mass, pray, etc. and look for the “next step”. That may be asking for advice, trying different summer jobs, taking a course in something you are considering etc.
Now I am going through a similar process. There is something I would like to do for a second career. I went in one direction that was more academic to try and start a debate on the concepts I have been studying. After about 8 rejections I have realized that I need to go in a different direction since I am really interested in being an entrepreneur more than an academic. So instead of sending articles to journals, I am sending a proposal to an agent.
So you have to be willing to iterate as well.
I started in engineering when I was younger.
Then I ended up in healthcare.