What should i do about this? please help?

I am 15 y/o male, nice-looking, but have skid-marks in my white briefs. I am always in a hurry when pooping and don't really wipe that well, plus I fart a lot, and I always have brown stains in the seat of my jockey shorts. My mom always checks my undershorts, which is embarrasing, especially when I come home from school with friends, guys and gals, and in front of my sister's girlfriends who are visiting at our house. When I come in from school she will make me drop my pants in the kitchen, right in front of my friends and her lady-friends, and she will make me come over to the kitchen table where she is sitting, and with my rear facing her, she will pull down my tighty-whitey undershorts and check for stains, which are usually there. She makes me walk around the house with my shorts down so everyone can see my skid marks, which is very embarrasing, because the women can all see my bare behind and my privates in front. I can wear a white t-shirt around the house, but I am not allowed to wear anything at all from the waist down, so that I won't get skid-marks in my briefs. This means that anyone who is visiting can always see my privates in front and my bare behind, which is humiliating, especially when I get a ***** and they can all see it sticking out.