I am finding that I am light headed lately after doing Liver Flush number 4. I am also on the herbs from sensible health. I don't have the yellow discolouration in my poop, but I also take chlorela and spirulina which makes it a bit green.

The yellow part in your stool sounds like stale bile is moving out, which is a good thing. The reason I say that is because I do the Andreas Moritz liver/gallbladder flush, and when I did my first one I had to prep by drinking one litre of apple juice a day for the first 6 days. I found my poop was yellow leading up to the liver flush, which Andreas said would be due to stale bile. I used the same protocol for my second liver flush... however I did not have the yellow eliminations leading to the flush. I also was not on chlorela and spirulina at the time leading to my second flush.

I would guess that you removed a blockage in the liver that can now detox old bile :)

Your response is normal. A Liver Flush will deplete your bile and thus stools afterwards will be less processed and paler or yellower. You are also leaking residual bile.
It is typical to have flares of physical and psychological symptoms following a good flush. Everything from head and body aches, to rashes, to rage and depression. You have released toxins which have been sequestered and are now working through, and hopefully out of, your system.
In my experience, feeling worse in the days after a productive flush is the norm, not the exception, and I tend to get better long-term results the worse the initial experience.
I have no experience with gentian, as I find herbs (and most other complementary supplements) to do me more harm than good.