Is this an orgasm? HELP ME PLEASE!

Meredith
Hi! I’ve been masturbating for six years now by hand, usually rubbing my clit, ever since I was twelve or so (I am eighteen now). I normally watch some sort of...media whilst doing so. After fifteen/twenty minutes I reach a point of excitation — at which I’ll experience a bit of throbbing, a sudden identifiable and instantaneous chemical release, and a clear-cut peak in the sensation. That threshold feels nice enough for me to have continued with this method for six years, but not good enough in any way for me to feel satisfied. I am bi but lean more towards the girl-loving side and I have never had sex.
This feeling I describe is very much localized in that one area of my body. It is a distinct physical and chemical moment, but I do not feel any sort of loss of control as most describe during orgasm. 
The thing is, though, that I do not think that this is an orgasm and I have never been able to achieve orgasm. I only make it to this point each time and then things settle down and I stop because going any further action is futile. 
Is this simply a ‘first checkpoint’ toward orgasm? An even more petit ‘le petit mort’ ? lol. I’ve tried going beyond and nothing works. I masturbate anywhere from one to three times a week, only using my hands because that’s what I have and the shower head has never worked for me. I am always completely in control of my body; there is no moaning or body movement besides that slight throbbing. Also, I should mention that my clit doesn’t seem very prominent; I have been thinking this might be a problem. It isn’t easily identifable and it’s pretty small.
Any input would be GREATLY appreciated.