Emmy is right, this diet is 'all or nothing' if you're having a hard time sticking to it then maybe you should re-think about a different diet not so strict. TFR is fab and it works FAST but only if you are 100% hun, if not you are just wasting your own time and money.
Reasons why you may be feeling sick and not seeing big weight losses:
1) Not drinking the recommended ammount of water per day
2) Leaving too long inbetween your shakes
3) Skipping shakes all together
4) Eating
5) Overdoing it with exercise or basic daily activities.
I got myself into a vicious cycle where I neglected my water intake, this effected me and the scales. It made going to the toilet a nightmare for me and totally disheartened me to continue but luckily I came through and am still 100% to this day. I've read a lot of people on this forum who experience discomfort or sickly feelings when they have had cheat days and had a snack here and there.. If you are worried maybe you should speak to the chemist or re-think this diet all together. Good luck x x x