Well, there is zero chance that your overnight weight gain was from food, as you need to burn about 3500 calories to burn one pound of fat. So conversely, you would have had to take in 24,500 calories. So it stands to reason that your body has reacted to something for that one weight gain. As for the gradual gain, I would guess that came from some sort of food reaction, or even something as simple as taking in more calories in a day than your body can burn (simple calories in = calories out). I personally am of the belief that simply taking hCG doesn't suddenly give your body "permission" to eat radically more calories than your body can burn efficiently on an ongoing basis; after being pregnant 5 times, I just feel that there has been enough hCG in my body off-and-on that it doesn't affect my body once it has all metabolized out.
You say you do have food allergies. What are they?
What is a macadamia nut day?