Question about first session

Hi everyone. I bought my first prostate massager today and tried it out a a little while ago. I didn’t notice anything for a while, so eventually I just relaxed and focused on my breathing, pulling it in on the in breath and relaxing on the out breath.

Eventually I started to get erect, the sensation got more intense, and my contractions got stronger involuntarily. It got to the point where I was moaning and shaking uncontrollably, but the sensation would then die down pretty quickly. I then relaxed and started over, and this happened a few times.

What frustrated me, though, was that this wasn’t exactly pleasurable. It felt like I was on the verge of an orgasm, but didn’t quite make it. Is this normal? Does the fact that I had masturbated a few hours earlier have something to do with this?