Ginger girl

I'm a 15 year old girl and I love holding my poo for as long as I can so I can enjoy the relief of it when I let it all out. I've had a few accidents but I'm pretty good at hiding them by washing out my knickers and putting them in inside the washing machine under a pile of other clothes.
Well last night I couldn't do that because it happened in my mum's car. I hadn't been in five days and when my mum picked me up from school, I was really desperate for a poo and it hurt to keep holding it. She could tell something was wrong with me and asked me if I needed to go to the toilet. I told her I did and I had a stomach ache. She asked me how long I'd been holding it for this time and I said it was five days. She was annoyed with me for holding it so long but she knew I was in pain and she suggested that I did it in my knickers as it would make me feel better. She added no one would know and I could clean up when we got home. I was shocked at first but my stomach was really hurting me and I knew the only way to relieve the pain would be to relieve my bowels but with no toilets around, I would have to do it in my knickers. I didn't really want to do that at first but I was so desperate I figured it wasn't so bad and if it got rid of the pain, it would be worth it. I felt my face burning red with embarrassment just thinking about it, but I decided to go through with it and relaxed my anus. I had to lift myself off the car seat a little and my mum opened the window as the tip of a huge turd pushed out my knickers. It was hard and bumpy and after about four inches was out, it bent over and broke off. It was quickly followed by more poo which broke up in my knickers and then it got a bit softer and smoother. It came out in a rush, filling my knickers before I could stop it. My stomach ache was gone but I still had to go quite badly. My mum couldn't believe I'd done so much poo and I still had to go a lot more. My hands were tiring from holding myself up off the seat and I knew I was going to have to sit down into the huge mess that had piled up in my knickers. I grimaced as I lowered my bum down into the fecal mass but it actually felt quite nice. It was a lot warmer than I expected it to be and really sticky.
Half an hour later, we were home and I was so glad to be in my own toilet. I locked the door and took off my clothes but not my knickers. I turned my back to the mirror to look at my bum and it was such a mess. I stepped into the shower and turned on the water but before I got cleaned up I remembered that I was still busting for a poo. I was so turned on I ended up masturbating as bits of poo fell onto the shower tray and I climaxed so much I found myself pushing and I finished my poo in my knickers. Most of it ended up in the shower and I had to pick it up and put it in the toilet. My knickers were ruined so they went in to toilet as well and I had a very long shower until I felt totally clean.