Hiya Christine and Joseph,
I read this post with interest, and beleive we may possibly be going down the same path. I am soon going to visit my uncle, who has already researched his family tree. He has already indicated to me that his gggrandfather was an o'Coghlan but dropped the O' and left Ireland in a hurry. He set up his family in the UK, but then left his family behind and set up a new family in Pennsylvania/Philadelphia area. How true this is, i'm unsure. But it could possibly be why I too am struggling to get beyond my 4th generation. I wish you luck in your search.
Andy Coghlan, Manchester UK.