Most commonly databases become large when you're storing a lot of data in them. That's about all we can tell you based on the (lack of) information you provided.
Try running this query on your database to see which tables store the most data (replace ${DB_NAME} with the actual name of your Q2A database):
SELECT table_schema, table_name, round(((data_length + index_length) / 1024 / 1024), 2) `Size (MB)` FROM information_schema.TABLES WHERE table_schema="${DB_NAME}" ORDER BY (data_length + index_length) DESC LIMIT 10;
That might provide some clues.
