If you have a visa stamped and extended every 90 days then you have a 90 day visa that can be extended. You do not have a 8 month, 9 month or any other longer term visa. If for any reason they decided to NOT stamp your visa then you would be going home. There are only a few long term visas available for people staying in Thailand and you don't have one. As Robert says you have a single entry ED visa that is extended.
So send the application and passport to the embassy in Canberra along with an express envelope to get it back. It is not really that difficult to do, just takes a bit of planning and getting the required documents together.
Nope no limit.....'officially'.....until an Immigration Officer has a bad day and pulls you up on it. Also I recommend staying away from Female agents.
If it "looked strange" then no one from any western country would ever use the 30 day exemption allowance. Do they want confirmed return tickets or only tickets leaving Thailand? If so book some cheap flights to somewhere or fully refundable flights.
So basically you didn't do your research and expected another 30 day extension after already getting one previously. Preparation and research is the key. ;)