15 that poops pants almost every day

i really dont know what to do, my 15 year old son poops in his pants around 10 times a week. i tried fiber, nope. i tried fruits, nope. i tried to get him on a schedule and that didn't work either. the strangest thing is that about one week every month there is no problem but the rest of the time is ridiculous. he doesn't get an urge to go at all it is just there all of a sudden. like bam. i dont understand how most of the time have so little control but then wow me by not for a week. so i thought maybe he just wants to get something out of it. i decided i would give hime a dollar a day for keeping his pants clean. well, i didn't get any underwear for the next 2 weeks in the laundry and figured that he was just hiding them. so i went upstairs and looked in the toybox and there they were about 20 pairs of absolute logs in each one. so if anyone knows anything that can help me. i am all ears and thank u Tweet