Hi,
To be honest I wouldn't recommend motilium in this context. Your placenta is producing progesterone which is blocking prolactin (the hormone that makes milk) and that is as it should be! Motilium works by increasing prolactin levels under normal circumstances, but it is not likely to be useful under this circumstance.
Your milk supply will dwindle. At this age your baby can have milk to drink in a cup if he is able to tolerate cows milk. No need to introduce formula. It is likely your little one will keep breastfeeding - milk isn't necessarily the main game here. It's all about comfort. It is also likely that the breastfeeding aversion will lessen as the pregnancy goes on. If you or your baby does wean you have done an excellent job, you should be really proud of breastfeeding so long and so well.