Crazy swings in insulin dosage requirements

So I want to know what other T1's think about this. I'm trying to keep a level head but I'm at my wit's end and need to find a resolution.

I have crazy changes in my basal rates and bolus ratios every few months or so. When I say crazy, I mean legit crazy like redrawing the whole basal. Last month my daily insulin use was 78u. Right now it's 48u.

I can go a few weeks with near perfect sugars then out of nowhere I'll start crashing at a particular time, or my bloods with shoot up at a particular time. No real warnings. Not prompted by a change in routine. My diet is pretty boring and diabetes friendly. They don't even correlate to my insulin use!

I'm pretty good at adjusting to compensate for these swings now, but I don't like treating the symptom of what may be an underlying problem. My research has uncovered a few possible causes (hormone deficiency, nutrient deficiencies, insulin resistance), but so far none of my doctors are willing to investigate, since I eventually get things under control after some tweaking and my hba1c is 6.9, which is good in their eyes (I vehemently disagree, but that's a different story).

As far as I'm concerned it's idiotic to ignore it. These bad sugars are debilitating. But this is one of those weird situations where the NHS stymies it's patients because I can't get bloods done without a doctor signing off on it. No chance getting a CGM on the NHS when my hba1c is "good".

Now a swing has happened twice in the past four weeks. I'm concerned that it's going to get more frequent. I'm also concerned it's the result of an underlying problem that may not have anything to do with diabetes.

Anyone have any experiences similar? Would appreciate advice or information, whether about my odd insulin requirements or about how to deal with my doctors!

Thanks