I have used hydroxyzine for itching and wonder if i can add doxepin as well?

Yes: Just beware of the additive side effects such as drowsiness , dry mouth, constipation etc.

Yes: Both are quite sedating, but Doxepin is the only one in my experience that causes weight gain, especially at doses 50 mg and above. If you start packing on weight , ask your doctor to try something else. Expect dry mouth, blurred vision, and possibly constipation, all of which can be treated with low dose bethanecol if necessary.