Coping With Canine Aggression

I adopted a 12 week old maltipoo back in January. He was orphaned and discovered running around in the country at 8-9 weeks old, starving and with intestinal issues. I’ve currently had him for about 4 months and during the last month or so, his aggression level has skyrocketed. He started growling and snapping at me in the mornings (yes I let him sleep in my bed, but I learned my lesson and not anymore). He was food aggressive when I first got him and worked with him on that.

Well, he got sick and I had to take him to the vet but about a week before that and after I got him home he wouldn’t let me near him without growling, snapping and biting. I couldn’t take it anymore so I calmly ventured through the biting and grabbed him by the back of the neck and laid him on his side. We went through this for about a good hour or more (he is one tough cookie). He’s now much more obedient, however, I do notice occasional flashbacks to his devilish nature. Now I wrap my hand around the back of his neck/shoulders and gently lay him on his side to make him submit whenever I feel he’s trying to be dominant. Am I doing the right thing? Or could I be making it worse in the long run? He’s also aggressive with most adults but LOVES kids!! I just don’t understand…