Mom,
I am sorry you are having so many pain issues and wish you quick relief. I take methotrexate for my Rheumatoid Arthritis. I take 40mg at one time 1x per week. I had pretty bad nausea the first few weeks, as well as some major headaches so suggest taking them when you have someone around to help out with the kiddos. I also chose to take them on Saturdays, when I don't have to do very much

They worked so-so on their own, but later formed the "base drug" for more advanced therapies (I now take Remicade every 4 weeks, which is used for RA and Chrones disease, and has been a Godsend...) I don't know if Remicade has been used for psoriatic arthritis or ms, but you may want to ask your rheumatologist. I wish you much luck with the methotrexate... the side effects I experienced did dramaticly subside after the first few weeks. I was told that taking them with a small meal was ok, and found that to also help.
I am currently fighting my own pain management battle, but have faith that the pain medications available now can make the world of difference.
I wish you much happiness and hope.
-Michelle