I'd say give it some time, it's towards the end of the school year for most people, so you have final exams and all that crap that can get in the way. If it persists through June, I believe it's time to start kicking people and recruiting players who don't lie about their activity just to get in a guild.
What we did to encourage activity was to plan events around the times we need players most, as well as try to give rewards for CW victories. Come up with some things people would like to do, they won't want to stick around much if they are bored.