Im skinny but my lower stomach sticks out a little?

Im 16, 5'6 1/2..and now im like 118-122 llbs. I dont know why but I had a flat stomach before and I weighed 115-117 and i just turned 16 in april. Im a person that has a fast metabolism and i never gain weight except for when i grow in height..Ive noticed recently like 3 months ago my stomach somehow went from flat to like a little puggy part bellow my belly on? I was just wondering what caused it to become puggy? I mean above it i have abs still??? I dont havint i there i miss how my stomach use to look and idk what its from? i also started to like bloat way more then i use to after I eat? :T