346. Katy Perry - Birthday
Birthday is doing just fine.
If you compare with LFN, it's nearly on par with its digital performance. It didn't enter the top 200 until 3 weeks after radios started to play it in early May 2011 (the adds date wasn't even until June 2011

). It had a slow and progressive rise to the top 50/100, and we all know what happened after the video

Given the fact that it was a 5th single, the pre-video iTunes performance for LFN was great. Looks like Birthday is following that similar route.
tl;dr don't freak out over Birthday's slow rise. It's obviously going to be much more difficult for the single sales to be as strong as a lead single would perform.