Adopted dog snaps at owner several times in 6 weeks.

Adopted a dog from the pound. 10 month old, 22 pound mutt (probably chihuahua and something else). Had him for 6 weeks.

First problem is reactivity. Barks and lunges at other people and especially other dogs on walks. Wouldn't stop barking at visitors and relatives. Accidently ran out my door without a leash twice. Barked at the mailman and another person but stopped lunging a few feet away.

Has possible separation anxiety but that is improving. When I leave, WIFI camera shows he would whimper and howl for half an hour and then go to sleep.

Very affectionate dog and follows me everywhere. However, snaps at me on several occasion. When I try to get it off my bed by grabbing his collar. When I touched his paws and nails just to get accustomed to nail cutting. When I a gave it a smooch on the head. He didn't bite me, but his tooth did scratch my forehead.

Barks and whimpers all night when I leave it in his play pen or when I let it loose but shut my bedroom door.

Am I expecting prescribed behavioral medication to fix this? I'm thinking of returning him to the shelter. It's only been 6 weeks, and I don't want him to bond with me too much. It's a small, young dog which often get adopted quickly. I live alone, so I figured a family can handle these problems better.