I didn't have hives but I was diagnosed with contact dermatitis which is a fancy way of saying my skin didn't like something and my dermatologist tried tracing it back to any laundry detergents, lotions, and even shampoos because they run down your body in shower.
Like the above poster said it could be a new development of a food allergy. Or an old or new medication can cause hives. Many members here have posted that they were on medications for years and suddenly they had a reaction to it, out of the blue.
When I couldn't find any trigger I took over the counter antihistamines and used anti-itch creams. If your hives are severe it could also cause breathing issues so stay alert. Please let us know if you discover anything. 🤗
Mine were caused by gluten intolerance. You may have a food sensitivity.
I went to a naturopath and took supplements to detoxify my system which got rid of the hives slowly but surely.