Never cum while having sex with a guy or a girl but I can while I masterbate myself, Is that normal?

So I’m 16 and I’ve been with around 10 guys and a few girls and NO ONE has ever been able to make me cum! But when I’m going down on myself, I can within 20 mins. So weird idk what to do. The sex feels good but they always finish and I don’t and I always fake it 🥴

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