I have the same thing going on. Does the dryness only affect your mouth? I ask because a number of years ago diagnosed with Sjogrens Syndrome. I personally find articificial saliva works for me. A lot of the time if I have not got the preparation, I do tend to devour - literally - iced lollipops which I find better than drinking lots of water.
The thing with Sjogrens though is that it doesn't only affect your mouth, it affects other parts of your body. The other 'main' one being your eyes. Here is a brief overview of it - I hope I have made it clear to understand :-
It is a chronic autoimmune disease in which people’s white blood cells attack their moisture-producing glands. Although the hallmark symptoms are dry eyes and dry mouth, Sjogrens may also cause dysfunction of other organs. Extreme fatigue and joint pain can also be experienced.
About half of the time Sjogrens syndrome occurs alone, and the other half it occurs in the presence of another autoimmune connective tissue disease such as rheumatoid arthritis, lupus, or scleroderma. When Sjogrens occurs alone, it is referred to as 'primary Sjogrens'. When it occurs with another connective tissue disease, it is referred to as 'secondary Sjogrens'.
So it is not because a person has lupus that they can develop Sjogrens. As previously said, it can occur without any autoimmune problems.
I'm sorry to say but your rheumie seems a bit dismissive to say it is nothing. If the 'dryness' is affecting you in other ways, then a few simple tests would be all that was needed to confirm or discount Sjogrens.
If you need any more help on this, plese let me know.