Can't "climax"

I can't orgasm. Just can't. 
​I'm on the shot and apparently that's a common side effect.
​It used to bother my boyfriend because he felt like it was his fault, but almost 2 years later, it's obviously not from lack of trying. 
​We've tried SO MANY positions, toys, lubes, etc: nothing. It doesn't bother him anymore, thank god, but he's so sweet and keeps trying to find new ways to "get me there". 
​I never had sex before the shot so obviously I have no idea what I'm missing but, um, not gonna lie, it's still frustrating. 
​Especially because he's a fan of giving oral (I'm lucky, I know, most guys aren't) and I can't even fully enjoy it. 
​The most frustrating of all of it is the fact that sometimes, I actually feel a build like it might happen, the. It instantly vanishes out of nowhere without warning. 
​I've even looked up "tips", like relaxing and just letting things happen but nothing works. 
​I'm glad I've finally found a forum to discuss this in and let it all out.