13 year old male, Is it normal to get fatter during puberty?

I'm a 13 year old boy, I started puberty at about 12 years old and since then I started getting fatter. I used to be a bit skinny and my big brother who is now 16 is really skinny and kind of has a six pack but he barely does any exercise. I do a lot of sports but it never affects my weight. I feel a bit low on confidence because of my weight. It's kind of a bummer because there's a girl I like in school. I'm not overweight I'm just a bit chubby but I have moobs, not big ones ones but they are still a bit noticeable. I don't know if I will get skinnier and If I will how long it will take. I feel a bit jealous of my brother because he's always got a girlfriend. Not long ago he broke up with this girl and then a week later he got another girlfriend. It's also quite annoying because he's really skinny but he eats more than me. I don't eat a lot but I started eating more when I started puberty. Sometimes I worry that people won't like me because I'm a bit chubby. Sometimes I think I look a bit out of proportion because my face has always been skinny. I have a couple of friends who are quite skinny, Most of them obviously haven't gone through puberty but some of them have. I'm wondering weather I need to do more exercise, I started karate a couple of months ago and have really enjoyed it. It has improved my physical stamina but has nothing to my weight, in fact I seem to be getting heavier. I've weighed myself more often now that I've been more concerned about my weight and I now weigh about 9 1/2 stone. I feel a bit embarrassed because during P.E because boys wear shorts and my thighs jiggle a bit when I run and it's also annoying because at the start of P.E, we run past the girls P.E group which has a lot of skinny girls in it. Should I be worried because I'm not sure if I will get skinnier and my confidence is slowly getting lower. Can someone help please?