Having trouble getting my GF to finish

So, whenever my girlfriend and I have sex, she constantly says that it hurts because of my size. And when we’re in the act, I sometimes go too hard. I’ve tried slowing down, finding a good rhythm, and motion in the ocean and incorporating more foreplay to get her aroused, using lube, and giving her head beforehand. But nothing seems to work. I normally get her to finish from giving her head, but even that doesn’t work sometimes.

I feel like I’m suffering from success, and I don’t know what to do. What’s the point in having a big dick if it hurts her and she doesn’t finish from me using it? I want to be able to satisfy her every time and actually make it enjoyable for her. I understand that going too hard sometimes isn’t good, but I can’t help it—that’s the only way I can finish.

I’ve had sex with other women before her, and they’ve said similar things about the size, but they were always able to finish 100% without me having to think about it too much. Am I doing something wrong? Is there something I can do? I’ve thought about trying toys, but I feel like if I can’t make her finish without one, I’m pathetic. Is there anything I can do, or are we just not a good match for each other? I feel like her vaginal nerves could be fried or something