Your remedy is Sepia, id preferr that you used LM, as a waterpotence, in order to control and get rid of the psoriasis, in a controlled manner.
But fore a starter, use Sepia one M, one dose, once, avoid all types of vinegar and citrus,oranges, and plants containing acids, also coffe, and chocolate, coca cola for at least two months start stopping with this things, the day before taking Sepia, at least, pref two three days before.
Alos, do not supress the psoriasis,,its likely the supressing of it that causes the backpains.

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Homeopat MNNH Geir E.T. Marcussen
email: getm@eunet.no
http://www.homeopati.no