What is the ruling regarding the prayers I performed before I knew that semen is discharged with the tremor of intercourse, given that I used to think the fluid discharged was madhy (prostatic fluid)?

A woman's maniy (seminal fluid) is thin and yellow, though it may become white due to strong desire. Its odor is like that of a man's maniy, and one experiences pleasure upon its emission, followed by a weakening of the body's strength. If these characteristics do not apply to what you observed, then it is not considered maniy, and you are not required to perform ghusl (definition). Your previous prayers are valid. The tremor you mentioned is likely the minor pleasure that precedes madhiy (pre-seminal fluid), not maniy. Ghusl is only obligatory when maniy is discharged with its known characteristics.