I honestly don't know what I can do with a Masters degree in Theology.
Other than teaching in a Catholic university or Seminary, is there any other jobs that I can do? Is serving God as a layperson an impossible task to do?
You won't be able to teach at a Catholic university or seminary with a master's degree in theology. That's almost certain--there could be some exceptions, but they're getting more and more rare, and what exceptions there are now tend to be part-time and/or temporary positions, rather than permanent, full-tie positions. There are too many people with PhD/STD's in theology for the jobs that are available, meaning not even every person with a terminal degree in the field is going to get a good job at the college level or higher. So to expect someone with just an MA to be competitive for such jobs is unreasonable. Again, no doubt one could point to certain exceptions, but they're exceptions, and it would unreasonable to expect to become such an exception oneself.
However, there are plenty of jobs available to people with master's degrees in theology. You could teach high school theology (chances are good that you could get a job and then take the required education courses while you're working, rather than needing to do an education degree ahead of time), or you could be a DRE at a parish, or you could get a job in a diocesan office--the respect life office, or something, for example--or you could become a book editor at a Catholic press, or any number of things.
The thing to do right now, I would suggest, is to continue on in your studies, since you seem to think that God called you to them for the time being, and see what doors open up for you. In other words, stop worrying about the future (to whatever extent that's possible) and just focus on being a good student. But that doesn't mean you can't give some consideration to future plans. If you're currently in a graduate program in theology (sounds like you are), then they should have some kind of placement office of some kind. Talk with them and see if they can start pointing you in the right direction. Chances are that they get job opening listings from local parishes and schools and the dioceses around the area. They should post those for their students to see. This will help you get a handle on what the possibilities are.