Oh no! Justin Bieber hit Twitter on Sunday to let his fans know that due to travel and a change in weather, he's consequently feeling under the weather. And right before he's due to perform on the 'Christmas in Washingon' special! Don't worry though, Beliebers -- Justin knows the show must go on. After all, it's the President! The Biebs will perform as expected, because a little cold never stopped him. That's good news for Victoria Justice, who is really looking forward to her appearance as well, according to her tweets. Also on Twitter, Jennette McCurdy made herself a Sunday trending topic by doing a live Q&A, while 'Glee' famer Harry Shum Jr. taught us the wonders of the rise and dine, Wiz Khalifa tweeted about trying new foods, prego Jessica Simson hosted a football party and Lupe Fiasco redefined hip-hop. See what your favorite pop stars were tweeting about today!