No furniture or appliance was delivered in April. But the weather started to get warm and humid in April. I hadn't dusted some areas (e.g. underneath the bed and window bays) for years. Maybe the dust and warm weather led to the outbreak.
Rentokil came 3 times to spray and fog, but that was just a waste of money. I just ordered TRI-JET-FOGGER & 2 GALLONS BEST YET from cedarcidestore.com (judging from their videos, I think this should work).
I still don't think the (invisible, jumping and/or flying) pest is bed bugs. My skin leaves no visible mark when I am bitten (bed bugs give a red mark).
I did something remarkable last night. I covered part of the parkay floor next to my air bed with a mosquito net. I felt hardly any pest on my bed sheet and I had a good night sleep. I think the creatures dwell in the parkay floor and the net prevents them from jumping/flying up.