Assuming you have not already been back to the doctor, getting checked out again is probably sensible. Not really sure how the Italian health system works , but hopefully basic medical treatment is easier to access than in the US.
If I had to guess, it sounds more like just a nasty virus with some post viral fatigue / symptoms, which is really pretty common and most of the time does not last that long.
But 3 weeks of feeling unwell is easily enough to justify getting checked out again, most likely you will not get a useful answer or anything that actually fixes the problem, but just excluding things that are treatable like iron deficiency and anaemia and diabetes etc is probably reasonable. Without more specific symptoms , the odds are there will not be a specific diagnosis to find, but that does not mean getting checked out is a bad idea.
Really hard to say if the tirz had anything to do with it now, sounds increasingly likely it was nothing to do with it but hard to be certain. It probably makes sense to wait on restarting tirz until you have been checked out and maybe on feeling a bit better, a calorie deficit is not likely to help feeling tired.
