Any experience with kids and TMS?

Hello...my soon to be 6 year old seems to have a sudden onset of seasonal allergies that I wonder if are TMS related. I am highly suspect of things like this that just appear. She had no history of allergies until this spring. I remember her having a very mild cold in late January/early February, then some time after that, maybe March, she starting waking up sneezing a lot. The sneezing and nasal congestion steadily worsened as spring moved to summer. Going outside seems to trigger it too now. We have thoroughly cleaned her room and bed, and put a HEPA filter in there. However, the sneezing and congestion persist. I did take her to a doctor who suspected seasonal allergies, but I just have a hard time accepting her explanation that allergies often just appear at random ages.

So...does anybody have any experience with their younger kids having issues that might be TMS related? I thought she was too young for this type of thing, but who knows. She has some learning disabilities and seems to be a little anxious. The symptoms did start around the same time as the shutdown. She did struggle with the routine change at first, and my wife has been very anxious herself about COVID. I'm sure some of that stress rubs off on my daughter.

I myself had a bad case of bronchitis that turned into and asthma and allergies diagnosis at age 9, but they are not an issue for me now. Looking back, I had some major mental angst going on then, so I figured it was likely mostly TMS. Please let me know if you have any similar experiences. Thanks...