Is it possible for me to get a dual or multi entry visa while in Thailand?

1. I am an American. I will come to Pattaya, Thailand on 28 December 2013.

2. I want to go on 1 February 2014. I will stay until 1 March 2013. Depart China and then return on 1 May 2014 and stay for a few months.

3. Is it possible for me to stay in Pattaya and send my passport and travel documents to an Agency for processing and then have it sent back to me in Pattaya?