I need some help, advice... anything at this point... so for a little over a year, my now 5 year old…

I need some help, advice... anything at this point... so for a little over a year, my now 5 year old son has been pooping in his pants... almost every day! I tried to help regulate him by setting a specific time for him to go every day and for awhile that was working, he was pooping the same time every night. Now I don't know what to do. I can't keep throwing away underwear.... (sorry but I'm not patient enough to want to clean the poop out of his underwear).... I'm sad and frustrated. My husband and I don't know what to do. We thought maybe it had to do with me being pregnant last year and then having his little brother (October 2016) but it has since continued... he plays and then doesn't want to stop playing to go to the bathroom, other times he said he didn't realize he pooped (hello, you don't feel a lump of crap in your underwear?!) other times he will poop and the poop is like a foot long and a thick as a coke can.... what do I do?? He starts kindergarten this fall and I'm afraid it will just continue at school and this can't happen. He needs to stop. 😔