R.J.
Hint: Most minimum wage employees of healthfood stores don't have degrees in neurology or herbal pharmacology or endocrinology or even any coursework in those fields. ;)
As in... ignore them.
ANY substance, ESPECIALLY a concentrated chemical hitting your system, can cause headaches. Even chemicals that are supposed to ease headaches can cause headaches in some individuals. The chemicals hit our bloodstream, and go smacking up against or through the blood brain barrier, and our body can't process them ... and voila. Headache. Or it messes with the dilation of the blood vessels. Headache. Or our liver starts sending out warning signals. Headache. Or, or, or. Seriously. ANY substance can cause headaches. It's a sign that either the chemical or the dose is wrong.
((Healthfood/Supplement places crack me up. I can't tell you How Many Times -by both min wage employees and owners alike- I've been told... "Oh! There are no chemicals in these!" when I'm reading the back of something. Hon... these are nothing BUT chemicals!! Proteins, lipids, carbohydrates (and the building blocks of each... amino acids, etc.), vitamins, and minerals... they're ALL chemicals. In fact, the less refined you go the MORE chemicals are in them... because you have all of the akaloids, resins, sugars, salts, etc. that make up the rest of the plant or substance.))
If you want to do some empirical testing (wait a few weeks, and try again), by all means. Be prepared for a headache, however.
Is it ALL connected? Possibly. Most likely, however, your body can't process one or more of the ingredients the way that it used to and you're having a reaction to either a specific ingredient or the massive dump of them into your system.
"Headache wouldn't be a side effect." Bwahahahahaaaaa. Seriously??? Whomever you were talking to needs to go take a very basic introduction into human physiology.