how can I fight the fatigue and lack of desire that RA has caused ?

 Try asking your employer if you can sit at your work station or else try some bench work that you could do sitting down. He should have some alternative if he can understand your situation at all. Try water therapy, ie. swimming , which is very relaxing and does'nt require much energy if you do just a minimum. Have a look at your diet and make sure you are eating the right foods as you may be adding to the pain further. I replied to a woman recently about diet and you can look at that letter and see the results.

Have you had your Vitamin D levels checked?   I had the same problems.  I now take vitamin D supplement and it has helped a great deal.

I would suggest you talk to your rheumatologist about your problem to see if they have any suggestions. As well, check out my post on working with RA for links to resources that may help you develop accommodations to make your job easier on your body. You may also want to think about changing the kind of work you do - a couple months ago, I wrote a post on going back to school that might leave you some ideas on things you can do to keep working.