It could be that you're quite intense and appear to be holding back something, when a subject in an interview isn't welcomed. Tune in to your interviewer(s), who could see this task as interfering with their "real" work. To accommodate that person, keep your answers to questions posed, concise and to the point. Whatever you do, don't ramble on with anecdotal incidents. If a question seems unclear, simply ask what the interviewer wants to know about whatever that is about, without appearing to doubt their ability. A good way to get more information that allows you time to get your thoughts together, might be to respond with a query about how they want you to phrase yoyr answer, with some experience or knowledge. It's easy to be led astray with lack of clarity, getting on a track that wasn't the intention of the questioner.
Above all, keep the atmosphere as light as possible, without telling jokes or appearing to know more than the interviewer. You want to come over as someone they'd like to have working with them, not a doubter in their ability to lead. Interviewing can be onerous, with one applicant appearing similar to all the others. Wear something clean that you know sets off your appearance well and isn't over dressy. Since nurses usually wear scrubs to work, you need to present yourself casually, yet in line with any work environment on any day that isn't Friday (when overly casual dress is accepted). Keep makeup to a minimum, as you'll not be interviewed for your cosmetic skills (avoid "smoky" eyes.
Be sure to look comfortably, with a friendly expression, into each interviewer's eyes (not like a staring contest). Practice that in your mirror and with your family/friends, until you get that effect. It can be harder for some of us, to do that. The harder it feels, the more practice you need. In a way, you're lucky that you won't be rushing from a rushed work environment, into an interview. Be well rested (bloodshot eyes may be like warning lights to a prospective boss.
At most Federal Employment offices (formerly called "unemployment" offices), there is a "Profile" Club for professionals. That's got a wealth of employment information, and classes for improving how your CV looks, and role playing interviewing situations with others who are your peers! That place is an opportunity to feel less isolated when you're not working. Even if you need to hire a babysitter to get out of your house, it's well worth doing that! Consider it a job requirement.