Nicole Cartmell had not been seen since Valentine's Day, The Sun reported. Her parents were babysitting her 6-week-old son and she never showed up to collect him.
Two young men, one of them believed to be Cartmell's boyfriend, Steven Devesey, 20, were held for questioning Thursday. Devesey reportedly told police before the body was found that he had not seen Cartmell since they had a fight on Valentine's Day.
Police said officers went to the house because Cartmell's bank card had been used since she vanished. They noticed a bad smell.
Neighbors said they had heard frequent fights.
"She just disappeared off the face of the earth a few weeks ago," Abi Campbell said. "It's horrible to think she's been under the floorboards. They moved in a few months ago and she was heavily pregnant."