Is what the questioner feels—wetness or coldness after looking at girls—and his going to check without finding anything, considered a [form of] Waswās (obsessive whispering)? And what should he do if he finds madhy (pre-ejaculatory fluid) after the subsequent prayer, having checked earlier and found nothing? And does he have to repeat the previous prayer?

If you suspect the emission of pre-seminal fluid (madhy), you are not required to investigate. It is sufficient for you to act based on the original presumption, which is its non-emission, in order to avoid obsessive doubts (waswas). However, if you are certain of its emission, then purify it from your body and clothes, and perform ablution (wudu') for prayer. If you see it after prayer, it should be attributed to the nearest time when its emission is probable. If its emission after the prayer is probable, then your prayer is valid.