When is it you feel the pain?
When you insert the nozzle?
As you are fulling up?
When you are trying to expell?
Each could be a different problem.
Keep in mind not everyone enjoys enemas. More people enjoy them that will admit to it, and few will discuss it as it's not a natural dinner table topic.
Take it slow. If your anal erotic at all, you should feel some enjoyment of the initial lubrication and nozzle insertion. If that feels good. expand on that.
If you feel pain during the insertion, stop doing whatever it is your doing, because something is wrong. Use a soft nozzle, or just a tube. Insert it a few inches and then start the flow.
If you feel pain during the flow, stop the flow. Do not place the bag more than a few feet above your butt. The pressure may be what is causing you trouble. Once you become accustom to enemas and you do enjoy them, you can increase the flow rate by raising the bag higher.
If you feel discomfort during the expelling, it could be because you are too full of either poop or the enema itself.
Try having a full bowel movement before you take the enema. Then only take about a pint of water. If things feel fine, take a second pint.
You will feel some cramps usually at about the first cup full of water. If you stop the flow it should pass very quickly as that is not very much water at all. As you feel a cramp, take a deep breath. Don't pant, and don't tighten your belly. Try to relax, take a deep breath and hold it. Bare down just every so slightly. If the cramp does not fade away, then expell the enema and try again in about 30 minutes.
The feeling you will eventually achieve will be a crampless filling with sensations of warm or cold surging into your belly depending on the temp of the water. You should be starting with water that is warm to the touch, not hot. Once you are able to easily take the enema, and understand how your body reacts, then you can vary the temp and pressure. When you are first learning to train your body to receive an enema, don't try doing stuff that people who have been taking them all their lives do. Everyone is different. Repear the things you find enjoyable, the goal is to pleasure yourself with the enema, not torture yourself.
I hope you are successful. Trying it yourself in a quiet setting where you are comfortable and relaxed should go a long way in making it enjoyable for you.
Slow