Margo's got troubles aplenty in "Margo's Got Money Troubles," a plucky, amusing, somewhat dirty, distinctly un-erotic novel by Rufi Thorpe. She's 19. She has a baby whose father, her English professor, makes her sign a nondisclosure agreement. Two of her three roommates flee, leaving her in the lurch. Her father, a drug-addicted professional wrestling celebrity, moves in. She loses her waitressing job after missing too many hours.