Despite a healthy diet and medium level activity I have gained 5st in 6 months. Help!!!!?

My diet consists mainly of salads (no dressings) stir fry and fruit. I am constantly tired and have become very forgetful & clumsy. I walk an average of 8000-9000 steps each day which excludes exercise taken 3 times a week. My skin has become extremely dry, I have developed psoriasis (or something similar) on my feet, eyebrows?? and temples, and I have fine hair growth on my abdomen and . And despite my healthy diet, I am vitamin and mineral deficient! I don't drink or smoke and have no history of drug abuse. Does anyone have any ideas what could be wrong? Thanks.