AceShowbiz -

Things don't look good between Scott Disick and girlfriend Sofia Richie. A new report from PEOPLE has emerged suggesting that the 34-year-old restaurateur and the 19-year-old model's "relationship is starting to fizzle." A source tells the website that "they're starting to argue more, and it's bothering Sofia."

Sofia allegedly thought Scott "would be more serious about their relationship and is finding herself to be more frustrated with him as time goes on." The source says, "Everything everyone has been telling her to look out for, she's now starting to see for herself," adding that "it's really upsetting for her, but she is trying to work through it."

Scott and Sofia first sparked romance rumors when they were pictured cuddling up aboard a yacht in the South of France during the Cannes Film Festival in May. At the time, the model daughter of Lionel Richie denied anything romantic was going on between her and the reality TV star, insisting that they're "just homies."

But a source said in mid-September that they had become "inseparable." The duo finally confirmed their romance via social media later that month, flaunting major PDA during a trip to Mexico. They've since been showing off their romance on and off social media.

Late last month, it's reported that Scott has also been "constantly" teasing Sofia about getting her pregnant. The Lord allegedly has baby fever following the Kardashian-Jenner sisters' pregnancy boom. "Seeing members of the Kardashian-Jenner clan getting pregnant, Scott jokes with Sofia all the time about what would happen if he ended up getting her pregnant -- even though he is in no rush to have children," an insider previously said.

But Scott's pregnancy quips were purely jokes, the source noted. "He loves to see the reactions on her face and thinks they're priceless," the source explained, adding that the former partner of Kourtney Kardashian is "a prankster in that way. But make no mistake, he's thoroughly enjoying the time he and her are spending together."