I'm close to your age, and I know how hard it is when the life you had seems to be slipping away from you, and you're not sure how to get it back. Your situation is especially hard because you don't the support of your family and friends. My siruation is a little different - I have four children and many family members who live close, so I sometimes feel a little smothered by the overprotectiveness, even though it comes from love and concern.
It can sometimes take a long time for plaquenil to kick in, so you may not be seeing the full benefits from it yet, but if it doesn't seem to be helping, it might be time to talk to your doctor about other medications like cellcept or imuran.
Do you think maybe it's time to let some of your friends know the "real you", the person who hurts, who is afraid, who isn't always the life of the party. I think your friends would like to know that person too, and there are many ways you can socialize and have fun without wearing yourself out. I know it's hard to reach out to other people for help - you don't want to impose on people, but I think you'll find your friends want to spend time with you, and won't really care if it's just delivery pizza and girltalk. Your friends may want to be more involved in your life, but be hesitant because they aren't sure how.
I also do a lot of work from home - it's great in terms of flexibility, but has the disadvantage of no co-workers around to trade ideas and proofread your work. I work in the legal field, and like you I worry a lot about errors because the consequences could be serious not only for me but for my clients. I try to work in small segments and recheck my work at least twice - I also do a lot of work at night because I'm a night owl and think better then. If you're having a real problem with daytime fatigue and inability to concentrate, you might talk to your doctor about a medication called provigil, which improves daytime alertness. Some people shouldn't take it, but you might ask your doctor whether it's appropriate for you.
And remember there are always people here to listen when you need to vent - sometimes a good online rant really helps!