Gas or movements??

Michelle • 21 year old FTM due January 2016 ❤️
Hi ! 
I know you guys get this question lots. But I'm 16 weeks and having trouble distinguishing if I'm feeling movements or gas.. I also have an anterior placenta which I heard can make me feel movements later...My question is: 
When you first felt something, were you certain it was movements? 
Thank you!