Orgasm without a toy?

Okay so I was wondering why it is so hard for me to have an orgasm? I feel like a get close when I am having sex with my fiance, but never do unless I use a vibrator on the clitoral area. I have faked an orgasm with him several times and I feel bad when I want to break out my little vibrator, but I want to have an orgasm when we are having sex. Also, I am a very mental person so I need to not only have stimulation on my clitoris, but I need to visual think about something that stimulates me to get me there. It just seems to take a while and it is frustrating. What can I do to have an orgasm without having to use a vibrator. I hear some woman have them just by using their finger, but that doesn't work for me, I need full-on, high powered vibration. Is something wrong with me? Maybe I'm using the vibrator too much and it is dulling my sensitivity there? Like I said I'm also a very mental person where thoughts about my fiance doing things really turns me on and gets me close to climaxing, but just not sure this is normal either. Please help. Also, is there anything I can take, a vitamin, or whatever that will help my libido and sensitivity even more? Thank you! K