Is the thick, clear fluid that is discharged with a gush due to lust considered semen (maniy), and is its emission considered puberty? What is the ruling concerning one from whom it is discharged, and will he be punished for an act committed at that time? What is the difference between divine punishment, psychological illness, and satanic whispers? And what is its expiation?

The fluid that exited you due to lust and ejaculation, and was thick in consistency, is semen (maniyy). If this is the case, then you have reached puberty. You are not required to be punished for this act; rather, you must repent from it and from all sins you have committed, for repentance expiates sins, and "the one who repents from sin is like one who has no sin." The intrusive thoughts that assail you are ploys from Satan to distract you from repentance, goodness, and inner peace, so you must ward them off and not obey Satan.