Hi Visperas,
If nobody else is going to take this one... I'll put in 2 cents worth!
This happens to me from time to time too, so I know what you're going through. It's no fun to have placed bets on the regimen (Having a life outside of CH) and then fall out of remission.
I'm sure Batch will chime in and probably run through the usual suspects... The 25(OH)D serum level test result will be perhaps a good start toward seeing what is going on, but there will be things you can do in the meantime I presume others will chime in with.
The addition of the 90 day course of B-50 Vitamins may help, as would the Diphenhydramine if you're having an allergic reaction, either apparent or sub-clinical. Unfortunately, I can't tolerate Diphenhydramine, even though I know it is hay fever or pollen allergy that pulls D3 from my system and CH remission collapses, but I sit my 25(OH)D3 level around 200nmol/l and it leaves a little room to ramp up D3 dosing when such an allergic reaction comes along. I throw down a 50,000IU loading dose at the first sign of trouble, and follow up with about a week of 20,000IU D3, the fall back to my 10,000iU per day, it works for me.
There's substantial room there to up the fishoil, and the Magnesium, maybe even the Vitamin C, but I would not offer advice on that as I don't know what the benefits would be.
I did have a lot of issues with different D3 brands. One study I've seen a few years ago suggests D3 labelling can vary from what's actually in the bottle substantially from 8%-146% (from memory, sorry cannot locate the study now), in the same bottle in some instances. I took truckloads of "Now foods" 10,000IU D3 for a few years and could not get my 25(OH)D3 serum level about about 160nmol/l, nor could I achieve CH remission.
Switched to another brand "Healthy Origins" out of the UK, this one here: (not an ad)
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With this one I've had 2 years consistent 25(OH)D3 results, and I was able to stay on 10,000IU per day for CH remission, only upping the dose to 20,000IU when I either fell below 200nmol/l or allergy/colds/injury became an immune system consumer for me. That's not very scientific, but it took 4 or 5 brands for me, before I found one that was both affordable and able to offer consistent serum lab test results over 200 nmol/l in my case.
Depending on which part of the world you're in, it may be allergy season as it currently is in the Southern Hemisphere. That may be a consumer and the reason why you're seeing an up-tic in frequency.
I'm unsure how the D3 regimen interacts with verapamil, but Batch has directions on his D3 regimen and dosing schedule thread concerning Verapamil.
If there's pollen around, or it's Autumn/Fall where you are, it may be sub-clinical allergy. I'm sure Batch will be along to help when he sees the post.
The good news is, there's a lot of info here on the site that addresses what you can do next, hopefully achieving CH remission. For some of us, this regimen does take a lot of tweaking and vigilance in doing so, to get it just right!
Good luck with it.