Update on the adverse effects of the antibiotics:
Tinnitus has (almost) gone back to baseline. I think it was a psychological effect. If someone is telling you a medication could worsen your tinnitus, there is a good chance that you actually feel it does even if there is actually no change. I was always hopeful that it's going to get better because ototoxicity (damage to the ears) after erythromycin has so far been reported mostly for older patients who took higher doses than I did.
The covering of the tongue has still not disappeared and has been identified as colonization by Haemophilus parainfluenzae, a low-virulence bacterium that usually doesn't pose any known danger to a person with intact immune system. The treatment is cleaning the tongue regularly and hoping that it disappears. Tests for candidiasis or other yeasts were negative.
Regarding allergies, the worst pollen to which I am allergic is rye and it was actually very mild this year. So while I seem to have picked up one or two new pollen allergies (probably birch and beech) after the antibiotics (causality is unclear), the worst preexisting allergy doesn't seem to have gotten worse, which is a very good news.
Last small thing as a side note: A blood clot is still jamming one of the veins on the back of my hand where the needle was. My sister who is a doctor in training says it's going to disappear and blood flow will normalize again, but after almost 3 months it still hasn't. It isn't causing me any pain or discomfort and my sister says it's nothing to worry about. But it still strange to see all you veins in your hand fill with blood, but one doesn't.
So the adverse effects - at least those I am aware of - have been limited and seem to be getting better and I am hopeful they will all go away.
I would still advise everyone to carefully consider a decision to take high-dose antibiotics. Although it seems to have turned out OK in my case, it is definitely not risk-free, even if it is a usually well-tolerated antibiotic.