I have had Long COVID for over 3 years. I have Sjogren's Syndrome that causes the symptoms you stated about your glands and facial swelling. In addition to pain and swelling my teeth started falling out. I had to have 2 oral surgeries last month. I suggest that you have a biopsy of your salivary glands to get tested for Sjogren's Syndrome. I would not recommend relying on the blood test for accurate results. Sjogren's can impact other areas of your body. Johns Hopkins is seeing their long COVID patients with POTS also being diagnosed with Sjogren's Syndrome. I have POTS. No idea why we are getting both. Good Luck. Take care of yourself and err on the side of caution when you start having any new symptoms.