After the Advil starts to wear off I get nasal congestion, headache, fatigue and what’s weird is lower back pain. I’ve never had a back pain issue. The fatigue can even come after a nap. These symptoms are daily.
I'm so sorry that is happening! As you probably already know, Advil (NSAIDs in general) can cause adverse reactions in some people's pouches, which could be the source of the low back pain. I have had it from pouch inflammation before. I have also noticed that pain killers (even acetaminophen) make my pouch mad with repeated use.
Have you been to acupuncture? A knowledgeable Acupunturist can help balance the immune system to clear up stuff like long covid. They might have dietary recommendations as well. Your system needs help in recovering, but it can recover, it's just stuck in a bad pattern. Acupuncture has helped me so much over the years. BUT (at least in my experience) you have to find a practitioner that is a good fit for you. I have been to really experienced, respected practitioners who I don't mesh with (in the caregiver/care receiver way) and the treatment has been off. For me, gender seems to be a thing. I prefer same gender caregivers for most things because women innately understand my body system better. This has been pretty consistent. It's kind of like choosing a talk therapist.