Are you using some kind of powdered kefir starter or are you making your kefir from actual kefir grains (looks a little like cottage cheese or pieces of cauliflower)?
I use actual kefir grains and I didn't like the taste of it either. I tried adding sweetner and stuff, but that just made it taste more gross to me. Finally, I brewed it so it would be more sour with more carbonation. This was the ticket, though I didn't think it would be. Now it tastes like nothing (or milk) then just as I'm swallowing it has a nice lemon-like finish with the bubbles. I just drink it straight since that's what has turned out to be least objectionable to my taste buds.
Another thing I notice is that you will develop a taste for it if you keep drinking it. You should start out small anyway so you don't Herx too badly. As your intake grows, your taste for it will also grow.
If you are using kefir grains and want to know how to make it more sour and more carbonated, let me know.