I see this discussion hasn't had active comments in a while, but this is something I like to talk about.
I was diagnosed with PsA just after turning 23 years old and starting graduate school. I am now 24 and finished my first 1.5 years of grad school. I use enbrel and methotrexate, and sometimes walk with a cane.
Things you can do on your own to make life easier:
1) Take the elevator sometimes.
2) If you must write, get fat pens with grips. You can find them at any office supply store and they make writing so much easier!
3) Ask for help! Sometimes the littlest things are the most frustrating, such as opening a candy bar, picking something up off the ground, or reaching for an object up high. At school and at work, I casually ask for help all the time. People will help without even thinking about it, even at the grocery store. Ex: "Hey can you open this?" "Sure." End of conversation.
4) Be kind to yourself and others. Rest, and help others around you understand you need rest sometimes. Many people have never heard of PsA or are unaware that this is different than your grandma's arthritis. If a sibling, parent, teacher, friend, employer doesn't understand, teach them. Avoid self-pity or making them feel bad; help them understand PsA, and understand that you might not be up to your usual activity level sometimes. Tell them to google it or go to the National Psoriasis Foundation. I never had an issue here with friends or teachers, but I still have to remind my mom sometimes that I can't always have a full-activity day with hours of walking or being outside like I used to. And that is okay.
5) Continue learning. Understand PsA through and through the best you can by asking your rheumatologist and/or physical therapist questions, read about treatments or strategies online, keep track of your own progress and health, and stay on top of your medicine and exercises (whatever they may be for you!).
These tips are applicable at any age/stage in life, but are things I wish I had someone close to my age to tell me. You can and will get through school! Promise!