Epsom Salt *is* laxative. It should say so right on the label. So, yeah, you'll get diarrhea along with it.
Remember, you come here to take responsibility for your own health. If your body is that sensitive to epsom salt, then you could try using half the dose at each time, or you could take a single dose as you say. (Personally, I'd try half doses. Dr. Clark's write-up of how to do the flush shows that timing is important.) It's your body, and even the best advice in the world won't help you if it doesn't fit your situation.
So... take your own advice and cut back on the epsom salt. Then let us know how it went for you.