sounds pretty awful.
Diagnosing Lupus is really difficult, because most of the symptoms are subjective. However there are blood tests that are pretty specific to Lupus. Yet the problem with them is that they don't always show positive, even if you have Lupus! But if they ARE positive it is a clear indicator that something Lupus-y is going on. The problem is getting your doc to test you for them.
This is because doctors HATE patients telling them 'what they need'. Because 99% of the time, they are wrong. Docs see a lot of malingerers, hypochondriacs and people who just don't want to believe they have x disease, but want y or z because they mentally/socially cope with y or z better.
Doctors also HATE people who diagnose themselves via the internet. With things like lupus, the internet can really be helpful, but if you have ever googled your symptoms for a flu/virus and been convinced that you have leukaemia.... doctors have spent 6,7 years being trained on how to interpret symptoms (and more importantly, SIGNS which are things the doctor sees but the patient doesn't notice) and to be told by Joe Bloggs that they are wrong and Google is correct.... gets doctors' backs up very quickly.
My advice would be to go to your army doctor and be honest. (doctors hate people who aren't honest and have a secret agenda!) Say that your illness makes you think you can't continue in the army, that you desperately want to continue and need to sort this out no matter what it takes. (ie. this tells the doc that this is important and debilitating, and threatens your service)
Say that you've been so frustrated that you've been trying to figure this out yourself (not just "I've been googling my symptoms") and that you are really concerned that it's more than just arthritis, and you are especially concerned that it could be this related condition, Lupus. (not "I have diagnosed myself with Lupus")
Your doc will probs sigh and think "oh great, another guy who irrationally thinks he has an incredibly obscure illness" so say at some point that you really hope that it isn't Lupus because it's really nasty, attacks your kidneys and is difficult to treat and there's no cure ... but that you need answers so you can get treatment. (this tells the doc that you are realistic and not a hypochondriac).
Let the doc talk and ask questions and stuff, but make sure that by the end of the interview you say that there's a couple of blood tests that if they are positive, are pretty good indicators for Lupus - Anti-nuclear-antibodies (ANA) especially.
Now I don't know how expensive ANA testing is, but if orders it, and it does come back strongly positive, THAT is clear indication to be sent to a rheumy.
If the test comes back negative or if he won't order it, change tack and talk about the arthritis. Say that the meds just aren't working, and that all the docs are trying their hardest (a bit of flattery to soothe egos) but it all comes to naught. So you want to see an arthritis specialist.
Before you diagnose yourself with depression or low self-esteem, first make sure that you are not, in fact, just surrounded by a-holes.