cold, bitter herbs can disrupt the digestion

Jessers,

Mild thistle is a very bitter herb and its energetics are cold.
If you take a large amount of it with a meal you can disrupt your digestion, which will then make you very tired and produce toxins in the body from incomplete digestion.

The symptoms you describe, fatigue, weakness, chills, can be a sign of aggravating the vata dosha (as is anxiety). Your digestion is not strong enough to take a large dose of a bitter tonic without assistance from digestive enzymes or carminative herbs.

You could be allergic to the milk thistle, but this is rare. If you want to continue with the milk thistle, take it between meals and take some carminative herbs such as ginger, cumin, coriander and fennel, a digestive blend like trikatu or hingwastika or at a minimum, digestive enzymes with your meals to help you body along. Another option is to drink ginger tea with meals as this is warming and helpful for a weak digestion. You can buy ginger tea in tea bags for convenience. I like to make it with fresh ginger by peeling and chopping about 2 tbsp of fresh ginger root to a pint of water in a saucepan. Bring it just to a simmer then turn the heat off and let it sit for 10 - 15 minutes. Strain and drink. You can add a little honey to the cup if you like, just don't cook the honey.

You may want to read up on glutamine and consider supplementing with this amino acid as glutamine helps with the Sugar cravings/addictions. Glutamine will help repair the intestinal wall and thereby help prevent food allergies . It is also an enegy source for the brain. I take it to help keep my blood Sugar levels steady, reduce brain fog and increases my energy levels.

Hang in there!