If you are having to shrink files because you are running out of disk space then you need to get more disk space. Repeated shrink and grow of database files will harm your performance, whatever the reason is for why you are doing it.

If your log file is growing 'too big', how often are you doing a log backup? You may find that doing a log backup every 3 hours (or more often if needed) will stop your transaction log getting 'too big'.

If you are using Full Recovery or Bulk Logged Recovery, then you need to do log backups as well as database backups. Books Online (BOL) explains why this is necessary, and there are lots of forum posts on this subject you can find with Google.