I feel since you are experiencing side effects at certain doses you should discuss this with a doctor, not in online forums.

4k a day overtime is when you can get toxicity...

Most supplements are a tenth of that, and doctors usually won't recommend over 600/day...

You say you were taking 8k a day bro.

Even the 50k/14 days is just under when toxicity normally happens. But it's probably because you're pushing to take an absolutely insane amount and she wanted to first get you under the limit.

So I would like to know, in your opinion

Stop fucking asking random people and listen to your doctor.

The reason your blood levels is normal, is all that calcium is forming kidney stones. Those will be incredibly painful, and will teach you the lesson if you haven't learned it in a couple years.

Rule 5. Locking.

Vit D is one of the easier vitamins in that you have to take ridiculous amounts over a long period for it to be a problem, while really small doses once in a while can still be helpful.

1000mg daily is considered a lot and is used for treating a high/severe deficiency. Despite not being deficient to a diagnostic degree I take a pill now and then (every few days, whenever I remember) to make sure I'm not deficient, since my region doesn't really get any sunlight this time of year. I guess it averages out to maybe 200mg daily.

Not a doctor and I don't have an exact answer to your question, but this might be helpful:

This may not be a thing in Italy, but check if you're actually able to get enough vitamin D naturally all times of the year where you are.

if you live in northern England near where I am, for example, you can only really guarantee you'll get your RDA of vitamin D from the sun during the summer months. I believe in north Scotland it's not ever possible to reliably get enough naturally.

I try to take a 3000/4000 (honestly which one depends what's on offer) more or less daily outside of summer. During summer I still take them but maybe every few days.

I would probably try what your doctor recommends (assuming you've already flagged your specific concerns, otherwise I'd do that first), it's entirely possible the 50,000 pill is formulated in such a way it manages to be (somewhat incredibly) slow release. If you experience any issues, schedule an appointment as soon as you can, so they can do some tests to help figure out what's going on. Your doctor has a degree in this stuff, so it's good to try what they suggest and discuss any changes with them

This also might not be much of an issue for you since I assume you're getting your supplements from the same, trusted place. But if not, there's a load of fake and low quality supplements out there, make sure you research the brand you're getting has been tested and had its contents verified independently. Any issues could be down to unexpected adulterants rather than the vitamin dose itself