You need to be patient. Unless you pay to have your site crawled every 48 hrs then 1 month isn't long enough time to wait to start ranking in Yahoo for competitive terms.
i've gotten new sites ranked on yahoo in about 1-2 months for targetted (competitive) key phrases. it is possible.
at times i've had trouble getting yahoo to even index multiple pages within a month's time... and that's with lots of IBL's.
It isn't hard to rank for the lower competition keywords, but the high competition ones can be tough and I don't expect to see anything for them for 2-3 months.
For me, it seems that a change in meta tags, slows everything down and makes your results stagnate for a while.
Today Yahoo switched to somewhat new SERPS again. Don't know about your traffic from Yahoo but since 1 Jan one of my sites is hard to find in google And Y delivers nearly 70% of the traffic. And enough money to keep me adding fresh content and not to abondon this project. So I love Yahoo when they are not dancing and popping up doorways to the top.
I am seeing the exact same thing of late. Im getting referals for a new site every second day hopefully things stabilise.
Yahoo is very screwed up - it deindexing many sites.. Doesn't matter the type either... Linking forum