It sounds like you have stumbled upon the Italian giallo genre. While the title you provided seems to be a mix of a few different films, you are likely thinking of "Le scomunicate di San Valentino" (translated as The Sinful Nuns of Saint Valentine), which was released in 1974.
(Replace bracketed items with verified credits from the film master.) The sinful nuns of saint valentine - 1974 -DVD...
The film's explicit content and themes sparked controversy and censorship in several countries. In Italy, the film was initially banned due to its depiction of sex, violence, and abuse within a convent. Similarly, in the United States, the film was classified as an "X-rated" movie, limiting its distribution and exhibition. It sounds like you have stumbled upon the
Visual Aesthetics and Atmosphere