Cumming ?

So whenever I masturbate it doesn’t last that long (sometimes) whenever I feel like I’m going to come my legs tingle and my body kinda jerks but nothing comes out...I want to keep going but it’s to the point where it not pleasurable anymore..

what I’m trying to ask is if I am coming and what can I do to keep going (if that’s healthy)

And if I’m not coming how do I get to that point to pleasure myself to that extent.