It's usually low oestrogen levels. As oestrogen drops the body may become dry, inside and out. A good moisturiser may help to ease those areas that you can reach, I use 'vaseline' in the yellow bottle. 4 me it was itchy insteps: OK until I took off my socks at night, I would wake with one rough heel scratching the other !!
I 2nd Flossieteacake's recommendation of adding half a patch. Some find that keeping a mood/food/symptom diary useful too.