When I am having sex, I don't know when I cum. I know I do. I just don't know when. Does this mean I have a problem with my body?
If you know you are having orgasms, then chances are there's nothing wrong with your body in that respect. But you know you are having orgasms, but not exactly when it's happening, then it just means you are unfamiliar with all the sensations that come with your sexual response. You simply have to become familiar with those sensations so you can identify them.
Think of it this way. How do you know when you're thirsty? You just feel thirsty, right? Well, try to describe that feeling to somebody who has never felt thirst. Not easy, is it?
Likewise, you know your orgasm, but you're having trouble pin-pointing when it's happening. Well, you can try to identify signs. Most people would describe orgasm as an intense feeling with an abrupt release. Muscles clench. Skin flushes and sweats. Some people make noises or scream. And then they feel like they're letting go, and they have a rush of relief.
I think you can benefit from reading our article on orgasms: Sexual Response & Orgasm: A Users Guide. Then in time, you can try to familiarize yourself with your own orgasms. It doesn't have to be exactly what other people say it is. If you feel it, and you recognize it as your orgasm, then we're not going to tell you you're wrong.