Hi there,
I'm with Naomi, Anne and Anna. I say that because my DH works away a lot - for example he is away all of next week, back for 3/4 days and then again away for 3 days. In addition I have a step-daughter who lives with us half of the week and on alternate weekends. R who is 32m can find the changes unsettling especially if her sister and daddy are not there at the same time. The way we get around it is lots of reassurance from me re: how many sleeps until Mimi and/or daddy are home (whoever is the 'issue'), extra cuddles and attention if needed, phone calls to her sister so R's mind she is confident that she is still there and has not disappeared and FaceTime with daddy at BT or first thing in the morning.
I have never used Melanolin or any other type of meds to deal with this situation, which as I say for us in an ongoing one. And TBH i can't say i'd recommend it when there are so many other practical things that you can try and do for us at least seem to do the trick.
It may help you to know that as much as my step daughter being away with her Mother for half of the week is the norm in our house, R still has the same issues/concerns as to where her sister is. She is not one for change particularly and she will ask the same Q - where is Mimi mummy, I give her the answer and then the reassurance that she will be back in x amounts of sleep. She doesn't always like the answer and protests that she wants her sister back now, but does accept it once reassured
HTH xx