Medicated at bedtime... With what? At what time do the meds wear off? Just thinking he's sleeping til they wear off if paracetamol and then waking, so another dose may help.
Maybe try cutting your day back a bit like this:
7 wake
10 nap, 30 min
1:30 nap, up to 2hr
4hr A time
Bed, around 7:30.