MARIAH Carey and Nick Cannon's marriage is reportedly on the rocks. The couple - who tied the knot two months ago following a whirlwind six-month romance - are said to already be arguing about Mariah's demanding behavior. A source said: "Nick is basically around to attend to her diva-ish ways. When they were in Hawaii where Mariah was filming the video for 'I'll Be Lovin' U', Nick dashed off to buy her gifts at Tiffany and Co. and Louis Vuitton to keep her happy." When 39-year-old Mariah injured herself during the shoot, Nick was right by her side. The source added to OK magazine: "He helped Mariah out of the pool. She looked like she was going to cry." Mariah is also reportedly taking control of 27-year-old Nick's career, and is keen to promote his musical ability with high-profile performances. An insider said: "Nick had signed on to perform at a sweet-sixteen party before he and Mariah got married. But now Mariah needs to oversee and approve his career moves." "There are no more silly small-time gigs. She wants him to do big venues and projects. She definitely wears the pants in the relationship."                   - ES