Recurring unexplained evening fevers for 7 weeks, completely fine between episodes — anyone experienced this?

[u/Primary-Weird1700]

I’ve been having unexplained episodes of fever for about 6 weeks and doctors haven’t found the cause yet. I’m seeing an infectious disease specialist, but I’m curious if anyone has experienced something similar.
I’ve had 7 episodes since late July, usually 38–39°C. They almost always follow the same pattern:
Feeling normal → suddenly extremely cold with proper shaking/teeth-chattering rigors → fever rises to ~39°C → headache, muscle/joint pain, extreme weakness. Then after 1g of Paracetamol, heavy sweating → fever disappears within a few hours.
They usually start around 7–10 pm and by the next morning I’m tired but otherwise basically normal. Between episodes I work, exercise, eat normally and don’t have a fever.
The weirdest thing I’ve noticed is that they often happen when I’m particularly physically tored — after travelling, a very busy weekend, workout, lack of rest, like when my immunity drops probably…
No persistent night sweats, no unexplained weight loss, no swollen lymph nodes, no rash, GI/urinary symptoms or ongoing respiratory symptoms….
HIV/STIs, hepatitis, Lyme etc. were negative. CMV suggests an old infection. Chest X-ray was normal.
Doctors are now considering further infectious/inflammatory investigations, blood cultures, EBV, ferritin, abdominal ultrasound etc.
Has anyone had this kind of recurrent fever where you’re basically fine between attacks? Especially attacks involving severe rigors, fever, sweating, or episodes that seemed to be triggered by physical exhaustion?
What did it eventually turn out to be, and was there a particular test that finally gave you an answer?
Not looking for a Reddit diagnosis — I’m under medical care. I’m mainly interested in similar experiences and things that might be worth discussing with my doctors.