I'm not a girl but I'll try to answer it the best I can since guys also orgasm I guess the only way to tell is if you feel really really good after a while of playing with yourself. Like there's just a rush of pleasure and you feel like you're gunna erupt. It's easier to tell when guys cum tho, obviously.
Ok have you ever felt like you were gonna pee when masturbating? Have you ever felt you body tingle with pleasure, with wave after wave of bliss. This is what you would feel if you had an orgasim. It isn't easy to achieve though, trust me I know from experience. I have not had sex either, Virgin alert. When I had my first orgasim, I couldn't keep my eyes open. My whole body tensed and just pulsated. If you don't mind me asking, do you like to finger yourself? Because if you are feeling uncomfortable, then it isn't even worth doing. I have always been a fan of the water facet. It is easier to come and can be quite intense if you are not doing it daily to yourself. I hope this helps you a little. Don't be ashamed of masturbating though, I baby sit a 8 year old who always does it. Plus my six year old cousin does it.
Nothing to worry about betsy. At the sound of what you're doing, you are exploring yourself in a new way. At your age, your body, it seems, is changing everyday. You are changing from childhood to adulthood. Keep experimenting with what feels good, and don't be ashamed. Masturbating is a wonderful way to relieve stress and is something you can do for many, many years.