Have a photo on the fridge so his face is always there and he can say goodnight/morning to him. We used this and my SIL has also used this method when her DH was away for long stretches. Her DS was about the same age as yours.

Skype is another good way if it is allowed. This will also benefit you or family on the days you cannot visit.

You are an inspiration with will all you have to deal with Make sure you look after yourself in the coming weeks