Voldemort's resurrection doesn't give him his own body. Completely on accident... it merges him with Harry.
What happened next occurred within the space of a blink. Right when Voldemort had been certain of his body taking form... he'd been pulled away. Yanked, as if by a great hand.
He'd been dragged away from his cauldron and pulled through the air, the rudimentary body as well as his new one being left empty at the bottom of that cauldron.
Harry Potter was equally confused. At first, he'd been elated - he thought that the weird, pale baby-thing had actually drowned, just like he'd wanted. The pain from his scar had sizzled out-
-and then he (both of them) blinked.
Harry Potter's face flattened into something sinister before his brow furrowed slightly in confusion. With a burst of wandless magic, he escaped his bindings... and he had no clue how it was that he'd just done that.
His cold stare turned towards Pettigrew, who paled rapidly at the sight. His missing hand, that bleeding stump gushing blood, went forgotten.
"My- m-m-my l-lord?" He whispered, terrified.
Harry Potter's face blinked, slowly. His eyes remained cold, and sharp. "I'm not your lord, Wormtail." He hissed. The voice wasn't high, cruel, or cold... but it was sibilant. English spoken with a Parseltongue accent.
Wormtail was panting like a scared and dying animal.
"I don't know what I am, now." The thing wearing Harry Potter's body said. "I remember nothing of Lord Voldemort, and yet... I was him, except I am not. I remember everything of being Harry Potter, yet... I am not him, except I am."
With a lazy flick of his holly and phoenix feather wand, Wormtail was hung in the air by his ankle. The bloody stump gushed blood, pump-pump, pump-pump, in sync with the rat's beating heart.
"What have you done to me, Wormtail?"