Lupus is diagnosed by a collection of symptoms and bloodwork. So a negative ANA is not a definitive no for lupus.
You don't mention what Dr you are seeing. A rheumotologist is the Dr who diagnoses Lupus. If you are seeing a rheumy, perhaps you should get a second opinion.
Are you being treated for the IC? I have no idea if it is related to lupus or not, that is probably a question for your doctors.
Check out the Lupus Diagnosis link in my signature, that will help you determine if your symptoms are similar to lupus or not. Keep in mind that many diseases have overlapping symptoms so even if you have lupus symptoms you may not have lupus.
The most important thing is whether you are getting treatment that relieves your symptoms or not. The diagnosis is sometimes not nearly as important as feeling better!
Lynnwood, Lupus & Sjogren's ModeratorDIAGNOSING-LUPUS & LUPUS-RESOURCES
"Life is far too important to be taken seriously" - Oscar Wilde