Plus sized pregnancy question

Natalie
Okay, so im kind of a big girl and ive got a tummy on me. No lie,ive basically been holding it in for the last 5 odd years but now...im pregnant,lol. 
People normally start showing around 12 weeks and im coming up to 13 weeks now and finding it hard to hold in my belly anymore. But i dont think ive actually got a proper bump,i dunno. Anyone out there know ihow i can tell the difference between bump and fat??