As you are only interested in one sub, put the call as the first line in the sub and pass the Subname, set the limit to -1, this will log the whole stacktrace, you can limit it to as much as needed so you can see the information you want if there are too many items in the log.
This should show you where the call to the sub came from:
Sub SubtoTrace
LogStackTrace("SubtoTrace",-1)
.'Other code
.
.
End Sub
The first line of the stacktrace should show you the sub it was called from.