[eozei]

Actually, I don't think that you have a clinical problem. Have you tried not masturbating for a few days before having sex?

The other thing is that sex is a mostly mental thing -- you need to have the same mindset while you're masturbating as when you're having sex. Have you noticed how while masturbating you can stop ejaculating too by just thinking about something different? Try this.

Unfortunately for you, Singapore only has one sexologist (yes, this is a thing). But I really don't think you need to see her.