Stress is one HUGE factor in the immune system and the immune system, when low can trigger allergies. Hives CAN be triggered by stress and let's face it, our bodies are going through STRESS during menopausal changes! :)
Allergies are funny things. They can lay dormant, causing no problems until our stress levels are raised. Our moods can also affect stress levels in our bodies and menopause is a time of mood changes. So, it all goes hand in hand with raised reactions to certain things that we'd normally have very small allergic response to. Hives can also simply be the body's way of showing internal stress.
Have you tried relaxation therapies such as deep breathing, yoga, exercise, meditation or simply doing something that you truly enjoy doing more often? Do you have a support system to unload/vent to? Are you keeping your body healthy with healthy foods? Are you taking a multivitamin appropriate to your stage of life? If you're having personal problems that seem heavy on your mind, are you getting help to help you cope better with them? These are all things that can truly help. Hives are a symptom that something is going on within your body that is throwing your immune system out of whack to allergens. Try keeping a log of things that you've eaten, come in contact with etc., along with your feelings, emotions, moods and stress levels. You may find that it's combinations of things that cause it.
Let us know and update us if you find some other answers! It may help others as well.
By the way, if you do a search (top right hand corner of this page), on hives, you'll find that you're not alone with this problem. :)