Sounds like you need to do some transaction log management.

What is the output of this query

select recovery_model_desc, log_reuse_wait_desc from sys.databases where name = 'testdb'

And some reading material

Managing Transaction Logs - http://www.sqlservercentral.com/articles/Administration/64582/

Why is my transaction log full - http://www.sqlservercentral.com/articles/Transaction+Logs/72488/

Stairway to Transaction Log Management - http://www.sqlservercentral.com/stairway/73776/

Accidental DBA Guide - Chapter 8 - http://www.sqlservercentral.com/articles/books/76296/