Undiagnosed: Allergy symptoms without being allergic. Ideas?

Hello everybody,

I'm looking for ideas for the unexplained condition that I have had for the past half a year. Please, excuse my English since it's not my first language. At this point, I'm out of ideas, tired and hoping I might find someone who had a similar experience and might know what's going on.

Symptoms:
Eyelid swelling, red itchy rashes over my eyelids, bloodshot and itchy eyes, sneezing, coughing, throat ache and runny nose. Occasionally I have rashes on my body and face (hands, fingers, shoulders, chest, arms, legs, neck and forehead) and difficulty breathing. Recently I also experienced something that seemed like an asthma attack. It got better after 2 hours outside in the fresh air and two antihistamine pills.

It can get suddenly better, to the point that I'm almost completely okay to absolutely terrible in one day. Antihistamines seem to work the best.

How it started/other health issues:
It started along with the common flu and got terrible in one week. I was tested negative for covid. During this time I also struggled with sudden rapid heart rate – 140 beats per minute while being still. Normally I have around 70 beats per minute. This would happen at least 4 times a day for several minutes. Due to family anamnesis, my heart was checked and the results came out normal. After a few months, the rapid heart rate was gone on its own. A few months before the condition I had face shingles and herpes simplex on my lip multiple times during summer. I'm also watched for Hashimoto's thyroiditis. I have borderline results so I don't take any medication. I had eczema through my whole childhood and teenage years but I got rid of it 10 years ago.

Doctor examination:
When I visited my dermatology doctor I've been prescribed very mild corticosteroids that help with the redness but nothing else. I was examined and tested for allergies and the results were that I'm not allergic to anything.

What I already did and tried:
At first, I avoided for several weeks: sweets, chocolate, citruses, tomatoes, gluten, lactose, anything pre-made, alcohol, caffeine, high-histamine food in general, spicy and sour foods. It didn't make any difference. I continue to avoid or restrict all of these except gluten and lactose, just in case. What seemed to helped a bit is a low histamine diet but I'm not 100 % sure about the connection.
I focused on getting rid of dust mites. I exchanged the bedding, wash everything at 60°C, use anti-mites cleaners for mattresses, got rid of the carpets etc. I also exchanged the laundry detergent and stopped using cosmetics for 2 months but nothing resolved the problem.

I don't drink or smoke. I don't own a pet. I'm a sportswoman, I exercised up to 5 times a week before this condition and I eat healthy for most of my life. Except for this health struggle, I feel the happiest I've ever been in my life.

Thank you for reading this exhausting description and I'm looking forward to any answers!