Question about Nuva Ring

For the past month or so I've been dating a girl, and just the other day we decided to make our relationship official. Her current method of birth control is Nuva Ring. I've never had sex (knowingly) with a Nuva Ring user before, and I think I might be able to feel it when I'm inside of her... is this even possible? I'm above average in the length and thickness dept. so she, as well as pretty much every girl I've been with feels really tight, but something about this one feels different. I almost feel like I can feel the thing tightening or constricting my dick, when I get fully inside of her. The only position I don't really feel it is if we do doggy style where she lays flat on the bed with her legs together inside of mine. So far, IIRC, that's the only position I've been able to cum in. The past 2 times, I think I've felt it more and more, and I have not been able to cum. My girl gets off on cream pies, so I don't want this to become an issue. Am I imagining this thing clamping on the top of my dong or have other males experienced similar things?