I also had never heard of a woodwick candle, but apparently they are a thing, and are supposed to crackle and smell like a wood fire in the fireplace. Other than on birthday cakes, we don't really do candles at our house. Most of our lights are on a dimmer switch, and I don't care for the scented candles or the fire risk.
Silkie, you are wise to test, but unless he has additional symptoms you didn't mention, it sounds to me more like summer seasonal allergies.
The cats were sad and grumpy when I left the house today. They're not used to being alone all day.