Jo, just to share with you my experience with blisters and rashes, hope the info may be of help
I started my camino thinking I was prepared for blister prevention; socks liners and all. My little toe started having a conversation with me from day 1. As the days progressed, she recruited most of my other toes, soles, and heels. Walking with blisters (on both feet) was agony, but walk I did, everyday.
I eventually found the right formula - (1) vaseline my feet each morning and night. (2) each evening drain all blisters, and allow feet to air, and allow the wounds to dry up - this may mean sleeping without socks even when it was cold (3) my socks liners were not working for me - so out they went.
(1) & (2) an absolute must. (3) depends on individuals and materials of liners. It was almost 2.5 weeks before I could walk blister free, but I did, for the rest of the journey.
As for rashes and allergies. I suffer both from ezcema and uticaria, and am reactive to a number of things and situations, including weather conditions. I had been on trips where I had rashes covering almost my whole body and any clothing was painful. I had to be treated with steriod injections everyday to keep the infections down. It tooks me years to find the right formula. I now work on prevention and started my course of antihistamines on the same day I leave home up to the day I return.
I am not suggesting that you do this but you may wish to try to drop by the pharmacia, or the hospital, and have the rash tended to. And see if it is necessary for you to go on a course of antihistamines. Keep the rash covered with light gauze when you walk, to prevent dirt from getting into it, and leave it to air when you sleep (if possible), after cleaning it out with alcohol swaps or hot water.
I am allergic to wool. I get weeping rashes from almost within an hour the wool touches my skin. If you are allergic to wool you may need to drop by a shop and buy a new pair of socks. No cotton please.
And Falcon is absolutely right about nutrition. Try to have a good breakfast before you start your walk. For dinner, protein is important; for muscles to heal and restore itself in the night. Lunch, carbo and protein will give you the energy to continue. Carry a fruit/some chocolates with you to munch at mid morning and mid afternoon.
And dont forget to drink. Even if it means needing to use the public toilet along the way. Dehydration = fatigue
Rest well, eat well, hydrate well.
Small changes will make a world of a difference
Trust things will get better and you can enjoy the rest of the journey.
Keep well. Buen camino.