What to do with a dog that won't potty train?

I have a 6 month old, 5 and a half lb Poo Shi that will not potty train. i have been crate training since i got him at 6 wks old. i used to take him out every 30 min to an hr and gradually increased that time to up to 2 and a half hrs. he was doing pretty good when he was 4 months and only had a couple of accidents and stopped peeing in his crate at night. at that time i started letting him sleep in the bed with me. after a few wks he started having an accident every couple of days. now he has an accident at least once, sometimes twice a day. all he ever does is either poo on my rug randomly or pee on my bed usually while im watching tv or something and he is on the bed with me. he also will not develop any sign that he needs to go outside like he never pees in his crate anymore even when i was at wk for 9 hrs straight today. i got home from wk, took him outside for about 10 minand he peed twice, then i brought him back in to give him a bath. two hrs later we go outside for another 10 min and he does nothing. i come back inside to find he peed on my bed. i take him every 2-3 hrs, ive had him on a feeding schedule, i keep him close to me constantly and always in the same room if not right at my feet, i scold him when i catch him using the bathroom and then pick him up and run outside and put him in his spot to finish. the only thing i do that some people say not to do is put his nose near it and say no firmly and pat his then put him in his crate for 5 min. i take him out 30 min after he eats and drinks. i dont understand what im doing wrong, i have been thinking maybe it just hasnt been long enought but it has been 18 wks! im so tired of cleaning up messes, my room is starting to smell like urine, and im tired of changing the sheets every other day, if this does not get fixed soon im going to have to put him in a shelter or something which i really dont wanna do cuz i love him and my husband is gone 9 months out of the year and i have no children to keep me company. please somebody help me! i have cried over this issue enough i need help fixing it