Why can't i purge? ive tried a lot and its just not working!?

ive always tried purging when i over eat but for some reason i just cant! i just throw up this mucus-like stuff.. its weird.. anyways ive tried lots. it just doesnt work! does anybody know why i cant force myself to purge? :/ ive also tried ipecac. ive tried it once only because it was available, if i could get some i would most definetly use it, but its just become very scarce.. and please, i know the risks. so if you're hear to lecture me, dont even bother answering! i need actual advice that i ask for, and not your judgmental opinions. thank you!