If you’ve missed periods, you are perimenopausal. It’s likely that you are experiencing symptoms of less circulating estrogen. Hot flashes are the most common symptom from that, but the way we experience sex changes too. Medications taken for other conditions can compound the issue.
It is not unusual to for orgasms to differ in sensation as a reflection of differing stimulation. Using a warming lubricant may help with arousal, or considering localized (vaginal) estrogen could also help. To help with arousal with a partner, you can introduce new techniques or bonding behaviors. With a partner or on your own, you might experiment with erotica—either books or DVDs. You may want to use a vibrator, or if you've been using one and it doesn't seem to be helping any more, consider one that offers more stimulation.
Welcome to this new phase of sexual life!