Drastic Change in Y Ranking

Can someone help me figure it out?

[Eccus]

Hi:
Until very recently I was enjoying #2 ranking under my main keyphrase in yahoo search. Last week I started noticing my ranking falling several spots to #8 but this week I am down to #16.

The only things that I have done to the site is moving it to a better hosting and add more content pages to the site.

Has someone here experience the same problem as me? Can someone guide me as to why my ranking is going down?

Thanks a bunch for any help...