Thanks for writing in.
There are various causes of swollen tongue
and allergic reactions are among them.
In your case swollen tongue could be because of allergy
or dry mouth results from prolonged intake of lithium.
If this swollen tongue is sudden you need to seek immediate medical care with thorough examination,it could be a serious problem.
I would suggest you to consult a general physician and an oral and maxillofacial surgeon at the earliest to rule out a correct diagnosis.
Hope this will be helpful.