I don't know when I'm coming?

I swear when me and my boyfriend makeout (aka kissing, nipple stimulation, and fingering) I can't tell the difference between it just feeling good and me coming. And I know I've definitely come before. We just had sex for the first time today and I thought that MAYBE I would be able to tell a difference this time, but I still didn't. It frustrates me because from the moment we start to the moment we stop it feels the same way the entire time. Anyone know what's wrong with me?