You say that you're both excited and anxious about being with your partner, but that you're tense with him and haven't experienced this before. Let me first say that there's no magic pill that will solve this problem.
For women, sharing sexual intimacy requires the ultimate in trusting, giving, and sharing. This emotional component is just one part of a complex whole for women, but it's the place I'd start. I'm curious about whether you're tense with this partner in situations outside the bedroom, and whether you've been able to express your concern. It would be helpful it it's a problem you're looking to solve together rather than a "performance anxiety" issue for you alone. Being anxious about being able to experience orgasm only makes it more difficult!
You might consider seeing a therapist with a focus in sexuality to be sure that you're clear on the emotions and feelings you're experiencing.
If there is no emotional barrier to address, I've recommended Viagra or a very low dose of testosterone for women who have lost orgasm or intensity; both of these drugs are rescribed "off label," which means they're FDA-approved for another use.
I wonder whether you're able to experience orgasm with self-stimulation; if you haven't tried, I encourage you to. A vibrator used either alone or with your partner may provide the increased sensation you need. And if you're able to orgasm alone, you may learn some things about your response that you could share with your partner.
Sex is often complicated, with multiple interdependent components; it doesn't help that our bodies change as we gain years! Please do look to a therapist for any emotional considerations; if physical considerations remain, a health care provider knowledgeable about menopause can help you evaluate options. Most women in my practice are able to reclaim this part of their pleasure!