Hi !!
Our son is also 22 months and has been showing some signs of clinginess during the day and definitely at BT. Personally I wasn't too worried about it, but now that I see that your son is at the exact same age and is showing some similar signs, I thought I'd raise my hand and tell you.
Actually, we've also had a couple of nights of NW and BT fussing (he wants me to sleep with him, after being an independent sleeper, STTN for about a year). We've got a couple of canines coming down and a lot of new words and learning going on as well. I had put it down mostly to a change in season. Our work schedule changes drastically at this time too, and a visit from many relatives that we're enjoying. No illness here luckily.
I hope things improve for you... and for us. (Actually Tom slept TTN last night, so I guess things are already getting a bit better...)