Yorkie Papillon going crazy when no one present!! help!!

i have a yorkie papillon 12 wks old named Sammy. Hes a good dog most of the time. But everytime I leave him or I put him behind a gate he starts to cry first. Then after crying he sounds very angry and starts to rip things apart. For example today I went to school (which i'm usually only gone for 5-7 hours of the day) and came back to my bathroom (which i keep him in) all messy. In the bathroom I limit him to water, a bed, toy rope, and a puppy training pad. There isn't anything else he can get his teeth on other than these things. But when I came back the puppy training pad was almost in a thousand pieces, the bed was like upside down in a spot i didn't previously place it, but the water and toy were fine. I feel as if my dog has an anger problem , but i also thought of how he might just be teething. But then again he seems to always get angry and does these kinds of things when i put him behind the gate in the bathroom and do something else. I'll be going to training classes with Sammy later on this week, which I hope may help me to become a better owner. So if anyone can give me advice on what to do, I'd really appreciate it.[]