I am a male and after I took a shower earlier a large stretch mark showed up on my stomach , I havent gained weight or anything of the sort, why do they show up? I am 6 feet tall and I weigh 240 lbs, I am overweight but not very much, a lot of my weight is muscle, and my weight has gone up or down about 5 lbs, but never above 242, mostly down around 238,