Feeling baby or..?

So I'm 14 weeks and 3 days, ftm, I'm super thin and short. When I lay on my back I can feel where my uterus is at but there are times where I feel something and then there's a bulge in my uterus protruding out-- you can feel it from the outside. Sometimes the bulge is on the left end of my uterus, sometimes the middle it varies. Is that the baby or something else?? I also feel when the pressure is relieved too-- when the bulge goes away.