transient options build up

My site seems to gain a large number of transient option a day. which increases my database size by about 5mb a day until it gets to around 80mb and the site no longer loads.

I have to keep clearing the transient options and then flush the cache to reduce the database down to around 45mb. but that seems to also be growing a few mb a week even after clearing the transient options and cache. my database is currently 49mb a few days ago it was 46mb.

What could be causing this? its been dojng this for about 3 or 4 weeks now.

http://www.aussiedog.com.au