I'm sorry you are having a terrible time with this. I know everyone reacts to The Master Cleanse and the salt water cleanse differently.
However, here is what I think is going on.
You are still eating food! This will make you feel sick! And is extremely unhealthy.
Make sure you do not eat any food while on the fast. Only the lemonaid drink. And make sure you take the laxative tea at night. Too much of the laxative tea can also cause nausea.
One thing you can try is to just start off with the laxative tea at night, no salt water in the morning. After a couple days, give the salt water a try again.
I've had other friends try the fast and have the same effect you are having, but they would also cheat and eat some food while drinking the lemonaid. I've done it a couple times and it made me feel sick also. You are the only one who will pay for eating food while on the fast! There is nothing you can do about it except stay off the food and stay on the lemonaid.
Here's my suggestion, come off the fast. Go back to your regular eating habits. Re-read The Master Cleanse, and in a month or whenever you have a couple days off, start The Master Cleanse again.
If this is your first time, you may want to make sure you have a couple of free days for the first three days of the fast. Days where you can just rest in bed as your body begins to eliminate the toxins. After the first 3 days are over, the fast becomes very easy.
And when you start the fast... do not eat any food. It will make you sick and is extremely unhealthy and possibly dangerous. Like I said earlier in this post, please re-read The Master Cleanse. It is also very important to come off the fast slowly. OJ only on the first day (it will feel like a meal), and soup and fruits on the second day. You can have very unhealthy effects by shocking your body with food after coming off the fast.
One friend of mine did the same thing you are doing, and blamed it on the fast. He came back off the fast, and in about six months did it again, this time without eating anything but the juice. He had no problems and was very satisfied with the fast.
The important thing is to keep trying, to be patient with yourself and learn from what your body is telling you. You have already made a huge step with starting the fast. Most people never get to that point.