Welcome back !
Well, your concerns are justified in every sense . Yes , lithium and valproate may cause weight gain, and your apprehension is well conceded, but since you had mentioned that the muscle aches are having a toll on you and depression has again come back , so the only logical reason behind this all , was to change the precipitator that is Lamictal .
However, if you are so apprehensive about using Lithium or valproate , then do not worry we have other options as well , such as Carbamazepine , or the newest mood stabilizer , with the least side effects called as Oxcarbazepine , these two do not cause weight gain, so i propose you may opt for any of these 2 drugs , but i would suggest that you do this change in the presence of your doctor , and not when you are on a holiday , as although we do not expect any untoward side effects of these drugs , but , protocol says that any change in psychiatry drugs need to be done afer discussion with your doctor and in his/ her presence.
As far as duloxetine causing liver injury , well you are quite right in pointing out that , but , for this to happen one should be taking this drug for several years , which was never and will never be a case in your scenario , as we tend to keep you on this drug for 6-8 months and then taper it off , and finally stopping it . So, there is no need to be apprehensive about it's use, although being knowledgeable and cautious is always good. Also, the withdrawl symptoms of duloxetine , you are talking about , happen with all the SSRIs , BUT ,there is a way to prevent it , and that is never to stop an SSRI SUCH AS DULOXETINE, FLUOXETINE, PAROXETINE , SERTRALINE , ETC abruptly , out of sudden , these drugs need to be tapered slowly over a period of few weeks , before finally stopping it, and in this case there will no withdrawl symptoms. Also, having a drink occasionally would not do any harm , so do not take tension about it .Being a care giver yourself , i presume you would appreciate this point all the more.
However, i like to give patients options , so that they go home satisfied and without apprehension , so again , if you are apprehensive about taking duloxetine , then you may opt for an SNRI , called as Milnacipran , although it belongs to the same class to which effexor ( venlafaxine) belongs to , but it is a newer drug with least side effects and equal efficacy as effexor. So, you ,may start taking it , instead.
So, the new options for are ---
1)Carbamazepine or Oxcarazepine --- as a mood stabilizer , for replacing lamictal , these do not cause weight gain.
2)Milnacipran , anti depressant -- in place of duloxetine , if at all you still decide against the use of it.
So, i suggest you discuss the above mentioned drugs with your doctor first and do not start them on your own , as waiting for some more time would not cause any harm , but infact , it will only provide you with the best possible treatment option.
I wish you best of health and enjoy your trip , it definitely will act as a destressor.
I hope my answer serves your query according to your satisfaction.