Shan, have a look to see if you can find a dropper like this:
measure out his medicine on a sterile spoon or bowl and try trhe dropper - squeeze it into his cheek. i found kirsty was great with a dropper but choked and spat out everything with a syringe.
how does he nap in his pram if you are out walking? i have found that Kirsty will have a great sleep in the pram, I usually leave her out in the garden in her pram for her midday sleep, pop an insect net over it and he'll be fine outside. The fresh air helps them sleep longer for some bizarre reason. I also find the background noise of cars passing, birds tweeting, etc, helps her sleep better!
If it would work for him to have an hour or 2 in the pram in the garden, at least you'd get one decent sleep from him.
My friend's baby is just over a year and has taken every nap since birth in her pram outside (except if she's out in car or something).
p.s, use sterlising fluid to keep the dropper clean - not sure it can go in a micro steriliser, it might ,melt!
p.p.s. if he is reluctant to take his meds, try a few drops of your milk in it so its a bit more familiar tasting.