i started biting the insides of my lips, especially the bottom one, when i was about thirteen. first i had a blister and it bothered me so much i finally bit it off with my teeth. it hurt. then there were more blisters and i got used to it and it stopped hurting when i bit them off.
and then i kind of learned to like biting them off. i've always liked making things pop. so i started biting the insides of my lips even when i didnt have blisters. i know it's crazy but i've been doing it for decades. i do it usually once a day, i'm trying to cut it down now. although i do this every day, i usually only do it for a few minutes, although i used to do it for hours sometimes, especially when i couldnt fall asleep.
but only when i'm alone and i can stop myself, and never did it all day long.
i think part of asperger syndrom, or any other kind of autism, is being obssessive. like i used to walk on a branch that served as a bridge over a hole in the ground in the schoolyard as a child. like when my cat sat on my lap and he'd get off and refuse to come back if i swallowed. (he was very sensitive in his old age to the slightest movement.) so i felt i had to swallow every two minutes or so, and i tried hard not to, because i didnt want him to leave my lap, and that's made it worse, of course, and it was so hard till i felt i was choking. i get new obssessions and OCDs all the time.
there are obsessions and there are OCDs. we usually get both. i used to bite my lower lip pretty bad in the past, till sometimes it swelled and looked horrible, but still it didnt hurt. i dont do it anymore. there were other OCDs as well but if i tell all of them it would be too long a post.
that's what i think the cheek and lips biting is - some kind of OCD.