What is the theme in Portnoy's Complaint by Philip Roth?

Sexual expression—its necessity, its many variations, the appropriateness of those variations, and its meaning—is the key thematic element at the core of Portnoy's Complaint, and manifests in several ways. On one level, it is the main concern of its central character and narrator, who seems to have become almost frantically worried about his obsessions with masturbation, casual sexual encounters, and relationships that he feels he has to leave once their sexuality evolves in ways that do not agree with his ideas of what sexuality should be. On another level, boundaries-free sexuality becomes the primary means of his rebellion against the socio-spiritual-cultural values and customs of the conservative, relatively closed Jewish community in which he lives. On yet another level, the narrative clearly suggests that Alex sees the inappropriate sexualization of his relationship with his mother as a manifestation of those values, of the overly intimate, uncomfortably universal and inescapably pervasive control.