Keep your prescription with you, just in case, but I emphatically agree with the suggestions of getting your 3 months meds prior to departure.
Other than the great advice already given, I'd add keep to the Frances, as crowds are helpful environments for those with medical problems.
I'd suggest travelling as light as possible, rather than sending your pack along ahead of you with a transport service ; though I guess you could have both a small pack to keep always with you, including potential emergencies, plus a bag with your needed spares and extras that you could send on ahead. You'll have a clearer idea about your physical capabilities in the final weeks before departure.
Thing is though to plan ahead for those days when pain might prevent your walking or might keep your daily KM down below 10 -- including the possibility that you might start out thinking 15, but need to stop for your rest before reaching that goal. You wouldn't want to get stuck somewhere with your necessaries several K further down the road.
The ideal would of course be to have one or two companions willing to accompany you on your snail's pace Camino, and who could help carry your part of the burden -- another possibility though, for those of ill health, is a wheeled pack to drag behind you or push ahead rather than a pack to sling over your back.
Like this
http://www.gizmag.com/monowalker-hikingtrailer-backpack-trailer/17668/ or this
http://www.packwheel.com/ for example -- though I've seen models on the Camino that you can strap on, leaving your hands free for a stick or poles. I'd say dragging is better than pushing, given the terrain.
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Finally, walking with health problems and at snail's pace will sadly often leave you in situations of arriving late with no guarantee of a bed, so you'll need to plan for some contingencies of roughing it, or only staying in places where you can reserve ahead, or being prepared to shell out extra for hotel rooms.