I think what your experiencing is normal. Everyones detox process is different. On day 4 I felt like you. Currently I am on day 13 of a 30 day fast. Have some licorice or peppermint tea with honey. It is very comforting and warm. It helps. Don't force yourself to drink juice if you can't stomach it. However, try some sweeter juices. Carrot is supposed to be fantastic for nausea and stomach problems, try mixing it half and half with apple. Your stomach problems may be a symptom of your body detoxing. It may also mean you aren't consuming enough calories. You can also try organic vegetable broth. It doesn't have any calories though, so you won't get any energy, but you may prefer it to juice. Take it easy and rest today. Your appetite will return don't worry.
You are doing great. Is this a first time fast for you. This is for me. I have never done one before, so I am not an authority on symptoms, but I felt the same way.