I’m no sex expert. I just tell couples I am so I can sleep with the wife or girlfriend.
Sounds like a mental thing to me. She has climaxed with other guys? (don’t take it personally if so)
She also sounds like she’s holding back on opening up to you about the real issue. But that’s just my opinion, not an excuse to beat it out of her.:)
Try not stressing over it. You guys may just need to get over the hump (bad pun intended). The more pressure,the less likely it will happen. So be natural about it.
Try more time on foreplay.Not just the physical (because you seem to be doing that) but in the hours leading up to it as well,mentally and verbally. My ex gf would get worked up about my teasing her about what I wanted to do with her when we would be alone. Such as describing what we had done in the past, and how it made me feel etc.
Maybe she just needs more time to warm up than some girls. Hell, try a dirty video she might like, if she’s into that sort of thing. Once you manage the first one or two,the rest will likely be easier.
Good luck man,let us know how it goes. I’m sure the ladies can offer better advice than I can.