movement at 13w and 4d??

this is my second pregnancy and my stomach is pretty flat and i'm on the slimmer side so i don't know if that makes a difference, but i was laying down and felt pressure on my lower abdomen so i put my hand down and i felt a little bump! like just a couple inches maybe long, and i could also see it. my fiancé felt and saw it too. then it went away, could that have been my baby?? i haven't felt movement any other time like standing up or anything and i really didn't feel movement this time just pressure and saw/felt the bump. last pregnancy i had an anterior placenta so i didn't feel anything until 19.5 weeks and i don't know if i have an anterior placenta this time or not i forgot to ask