Side effect profiles vary from medication to medication and there are other mood stabilizers that have less of a potential for weight gain. As well although lithium is generally the mood stabilizer used first (being that it was the only medication developed specifically for bipolar, all the others were discovered to have that use afterwards but there still are many FDA approved first line mood stabilizers, this is a list of all mood stabilizers:
http://www.psycheducation.org/depression/meds/moodstabilizers.htm
For myself I found Lamictal far more tolerable that lithium and Tegetrol (which unlike lithium was of limited efficacy for me) and I did not have a problem with weight gain with it and it was effective but each person reacts different to each medication.
Thank u soo much for responding to my email, I will check out both the site and also check out Lamictal on the internet, once again I thank u for taking an interest to my questions..keep up the good work