Masturbation

I have a quick question. I know what can make me tremble and I’m breathless. But whenever I masturbate, I can never cum. At the beginning when I’m getting horny, I’m super wet. But when i’m doing it, it gets dryer and dryer the faster I go. Penetration doesn’t do anything for me, just clit stimulation. I’ve also never been penetrated. Why is this a delma for me? Why can I not cum? I’m literally shaking and I get none.