I usually have a flat stomach.. but now im all bloated? 17 female?

I’ve always been an average weight girl but with a flat stomach. I’ve never been to a gym and I don’t really diet. When I’m near my period I do bloat and eat a lot more which is normal but then I go back to my normal self after a week or so. I have a very fast metabolism too. However, im nowhere near my period and I know this is going to be tmi but I bloat an awful lot, my lower stomach fills with gas to the point it hurts and I haven’t been going to the toilet as much? I’ve gained one kg which I know isn’t a lot, (I’m 5’3 and usually weight 54/55kg) but now I’m like 56/57. I’m just concerned because even when I look in the mirror first thing in the morning, you can’t see my flat stomach. I just feel insecure. I know its only one or two kg but it affects me to the point i compare what to eat with other girls in my year. I cry at night and stress over it so much. I do overthink everything so I left it thinking it was a phase but I’ve been like this for almost a month or so. Whats wrong with me! I’m not pregnant and I haven’t changed or eaten more in my diet?I drink a lot more water now surely that should help! I just can’t sh*t as often and it’s getting me paranoid. Ive tried eating foods/nuts/berries etc to make me go to the toilet but no! nothing is changing !!! Someone please help and be nice! xx Thank you