yes it's common. My input would be to stick RELIGIOUSLY to the diet as outlined by Dr. Simeon. ON top of that drink large amounts of water (this depends on your weight...but I loosely say aim for more than a gallon.) What happens during this process assuming you are following it to a "T" is that in the exchange within the fat cells you are likely at a point where you have circulating fat and cells full of water. This can result in a "gain" if you are looking at the scale. Keep drinking to flush that water and you should see a decent drop. IT may take another 24-48 hours, but after this people can see anywhere from a 1-5 pound loss in just a day or two. What you will likely notice is that you are having more output than usual.
The other potential issue is if you are about to begin your cycle. If so, the same information applies. It's just water retention and will be released.
Of course this is all assuming that you are following Simeon's protocol and not one that is set forth by a clinic. Those are the instances that I have seen and heard of people failing. I'm not saying you are doing this, just putting it out there. Many clinics/doctors/books etc. have "tweaked" the protocol. I would strongly advise anyone to simply eat the foods in the quantities that he put forth.
JR-I have two that have and the answer is no. This is a TINY fraction of what would be circulating in your system during pregnancy. Especially if you do the homeopathic version. Even the injections and sublingual versions are teeny tiny quantities in comparison to pregnancy.