Keep in mind that the log can be bigger than the data size. It depends on transaction volume. I could have a 1MB database with 1 table, 1 row, 1 column, and if I update this value every second, my log will be larger than the data.

I'm guessing that you don't have log backups running. You should be running transaction log backups periodically, more often than database backups. I see many people running hourly if not more often.