Welcome to the forum pcampbell
I hope you will find the information very useful for your understanding of what's happening and making it easier to talk with your doctor, and the support useful for making the best of things.
Many people have a variety of symptoms of autoimmune connective tissue diseases of which SLE lupus is one. Most have 'inflammatory arthritis' as a feature Others are described and defined as rheumatoid arthritis, scleroderma, dermato/myositis, and Sjogren's is included because it has so many similar symptoms.
MCTD and UCTD both describe certain mixes of symptoms. Mixed Connective Tissue disease refers to an overlap condition with features of lupus, dermatomysositis/ mysositis, and scleroderma plus a few other typical findings such as 'sausage' fingers and Raynaud's, and on the lab side characterised by high levels of an antibody called anti RNP. Undifferentiated Connective Tissue Disease refers to an autoimmune connective tissue condition that doesn't have any specific features of the others: in the case of lupus this means no anti dsDNA antibodies or anti Sm antibodies and no biopsy proven skin or kidney problems. I am sure that many doctors simply diagnose ' lupus' often with the annoying prefix ' mild', meaning no organ damage.
With MCTD one of the conditions can come to predominate and with UCTD, although the majority stay the same, one of the distinct diagnoses might emerge over time.
In terms of treatment options these diagnoses make very little difference. In personal terms, it is best not to have an SLE diagnosis because of the dire effect this has on getting insurance.
Here is an article with more details about MCTD and UCTD
http://www.medicinenet.com/script/main/art.asp?articlekey=16955
If you are worried about seeming a baby you will not get the best possible treatment for yourself, to put it rather brutally. You have the right to get the best treatment available to improve your quality of life and keep it as normal and fulfilling as possible. If you don't tell your doctor about your pain she can't know and won't investigate the causes ( there are many sorts of pain and causes) and the most suitable remedies. There is nothing heroic or saintly about putting up with pain unless it can't be relieved any more effectively.
A good doctor will be concerned.
I suggest you get your blood test results and read up about diagnosis to get to know
your disease and why that diagnosis was arrived at. We'll help you all we can so you can live the best and most normal life possible with your symptoms well controlled.
Cheers
Clare