Does Depakote cause weight gain? Taking 500 MG twice day. Trying to determine source?

It can go either way:

Metabolic
Common (1% to 10%): Weight loss/Weight gain

It's very likely that Depakote is your cause. If your doctor determines that the weight gain is medically significant you might discuss switching to a different mood stabilizer.

Common Depakote side effects may include:

mild nausea or vomiting, mild stomach pain, diarrhea;

headache, mild dizziness, weakness, tremors;

problems with balance or walking;

blurred vision, double vision; or

changes in appetite, weight gain.

https://www.drugs.com/depakote.html