Agree with snailplane. 

Making it more clarified, as I read on a few boards, *since* preferably takes 'has/have' to state that the situation has remained from that point of time. 'After' dose not. 

So, 

> The situation **has** become worse **since** ... <br/> and <br/>The situation **became** worse **after**.... 

Agree with Frederik on 'gotten' as I see in [Oxford][1].

This [question's][2] answer is close and may be useful. 


  [1]: http://www.oxforddictionaries.com/definition/english/gotten?q=gotten
  [2]: https://english.stackexchange.com/questions/53302/do-thereafter-ever-after-and-ever-since-mean-the-same