Have had frequent urination, bladder pressure, lower back pain w spasms, chills/excessive sweating @ times. -uti, urine culture neg. what can this be?

Need to examine: It is not feasible to provide a meaningful opinion without examining you and may be doing some tests, including cystoscopy. There are non-bacterial causes of inflammation of the urinary bladder, including interstitial cystitis. Even tuberculosis can present "sterile" cystitis. It would be prudent to consult your urologist.

You should: probably have a PELVIC examination since it sounds like something iss putting pressure on your low back and bladder INTERNALLY..GYN visit is indicated! Hope this is helpful Dr Z