I had it recently, also my first time despite no doubt being exposed to it multiple times. 4 jabs, last in early July.
I tested positive for 11 days. Felt a bit rough the first few days - achey, fatigued, worse than a cold but not as bad as the worst bout of flu I've had. After a few days I felt better apart from a cough and blocked nose, and ongoing tiredness. I was getting very frustrated as everyone else in my household started testing negative after 3 days (my asymptomatic vaccinated 4yo who had just had his BionTech booster (after 2 Sinovac), and 8 days (the other adults with milder symptoms than mine), and 10 days (1yo, only had Sinovac).
At some point after a week or so I started getting sinus pain - bit of googling showed it's not a typical Covid symptom. On day 11 the pain was quite bad and so I had a remote consult with my GP who said that almost all his patients who are still testing positive by 10 days have had a sinus infection at the same time as Covid. His theory is it stops the Covid virus being cleared by the body and so continue to test positive on a RAT. He prescribed various drugs to clear my sinuses which gave me relief very quickly - 6 hours later I got my first negative RAT.
Another tip - the RATs the government gave us are way more sensitive than those we bought on HKTVMall. As far as I'm aware there's no rule saying you have to use the government RATs to get out of isolation.
Have no need it for it and I hate clutter on my phone