Hi HWP. and welcome to the forum!
If you have high histamine problems, I am not surprised that Vit C helps, because it helps to get rid of excess histamine, by boosting the activity of diamine oxydase, one of the two enzymes that eliminates histamine.
I often have excess histamine, and it usually manfiests as redness and itchiness in the eyes, itchiness on the skin, sneezing, and so on. What works for me, for excess histamine, is daily Vitamin C ( I take 250mg in the morning and 250mg in the afternoon), and my quercetin supplement ( 500mg quercetin, with bromelain, that helps the absorption of quercetin ). When I have more symptoms, I can add some naturals mast cells stabilizers ( mast cells are releasing histamine), like pine bark extract, L-Theanine, and others, because a combination of many is more efficient than a high dose of only one or two ( you can see a list of all the natural mast cells stabilizers I use at
http://poiscenter.com/forums/index.php?topic=2372.msg19856#msg19856 ).
You can see how I control my symptoms at
http://poiscenter.com/forums/index.php?topic=2090.msg16604#msg16604 . You could slowly develop your own pre-pack, by noting what works for you, keep it, and building up your pre-pack form there, slowly, through a patient work.