Possible coolant leak?

If you just topped it off and it is empty again then you are correct that you have a leak. The next thing is to find it. So you need to look on the ground for a leak and pressure test the system to try and narrow it down if there is an external leak. Here is a guide that will help with this:

https://youtu.be/W8kra65m15c

If there are no external leaks then we need to suspect it is a head gasket. So here is a guide that will show how to test for this:

https://www.2carpros.com/articles/head-gasket-blown-test

Please let us know if you have questions on this and what you find. Once we know where the coolant is going, we will know what needs to be done next. Thanks