Eeeek, so sorry you're feeling rough - as the Achren says above it does take some people longer to get into ketosis than others but I'm a bit troubled you're on day 8 and still feeling so bad. I definitely had those kind of symptoms around day 3 but they were gone by day 5.
I guess a couple of questions:
1. Are you tall? I think if you're 5'8 or other you should definitely be on 4 products not 3.
2. What was your diet like pre-Exante? I mean, if you were eating a lot per day or very carb or sugar heavy food your body might take a little bit longer to adjust.
3. Are you moderately active? Are you doing exercise or even a lot of walking/moving on top of taking your products?
Something you could also think about - even if you're not 5'8 - is going up to four products a day. Everybody's body is different, regardless of height, and 600 calories a day is just too small an amount for some people to function on. This is not, like, a bad thing. it's just a thing. I would seriously think about going up to 4 products a day at least for a week a two. 800 calories a day is still a significant calorie deficit and you will still get into ketosis and you will still definitely lose weight.
Please do not see going up to four products today as failing or letting yourself down or wussing out or anything like that: although VLCDs do definitely help you lose fat, they are not actually a race or a crash diet. You will be on the diet for several weeks. You must also be able to function in your life, otherwise you will not stick to it.
If you go up to four products and still feel shitty, I would maybe talk to a doctor?