I have a 5mo old morkie and he had separation anxiety and its back and worse then before....?

ello , I have a 5 month old Yorkie/ Maltese puppy. I have had him for three months and i have worked very hard in training him.I work 4 days a week and gone 8 hrs a day.He started separation anxiety a few weeks after i brought him home.I read and talked to trainers and studied like a collage course. It disappeared and he was doing great..house trained,alone time and very happy and stopped yelping. He has a good life with us and plenty of play time and walks and exercise as well. He is socialized with my friends dogs and has his own play dates.recently he started running at my feet again non stop and tries to get on me nonstop. All his training has disappeared as well...sit ,come,down,fetch .he will not listen and work with him daily even treats. he is shaking at times and vomiting sometimes and stresses him self out. I ignore when come home for 15 mins and crate trained and very comfortable huge two room place where he is in day when im at work. he was doing so well we could leave him with run of most of house and now he started going potty everywhere. so confused and getting exhausted. we have done dog training and seemed like a waist.HELP? thanks :)