7 month old started throwing tantrums and screaming when I'm not holding him?

Is this a normal development? What do i do??
This is VERY new, its like he's developed a whole new personality in the last 1.5 weeks. I want to approach this with the best knowledge and reactions, since how I react is really important for their behavior later. So far I've been trying to have him CALM himself (no moving or yelling) before I pick him up. He's gotten the hang of it when I say "calm, calm, calm, Still, still, still" gently. But he will be just fine until I walk into the room, then start sobbing for me to pick him up. If I dont, he will YELL and stamp his feet or legs, thrash around, etc.

HELP!