start itching at night, painless , no problem in peeing, never had sex, red spots on thigh
Anish, it is the red spots on your thigh that may give the biggest indication of what you have going on.
The good news is that you have not been sexually active, so you cannot have any sex related issues.
This sounds more like either a fungal infection on your skin or potentially a dermatological issue in terms of a reaction to something your skin is in contact with.
I wonder what it is you wear at night? Do you wear specific night time clothing?
You would also need to consider your hygiene practices - such as your own showering, whether you put on clean clothing daily, whether your bedding is washed regularly, and what it is your clothing is washed in.
So for example, if a poor quality washing powder was used to wash your clothes, the towels you use and your bedding with this may be causing significant irritation to your skin …