I'm almost 20 and I've been with my boyfriend for nearly two years... I've never had an orgasm, or at least I don't think I have ever had one. There are times where I get close, but it's hard to tell. 
A couple questions:
Will I know without a doubt when I have one?
Is it possible I might not be able to have them at this point in time? I'm always stressed and don't have great self confidence and I know that's a huge factor in being able to... And I've read online about the average age of a first orgasm being from about 20-27ish.