Been going to bathroom more frequently and urge is getting worse. bad lower back pain, no burning when urinating. what could be possible causes?

UTI?: Urinary tract infection probably is the best bet, despite lack of painful urination. Several other possibilities as well, such as pelvic or other intra-abdominal infection, kidney stone, and others. It could be serious. See a doctor ASAP. If you also have fever, do it immediately, even with nighttime and the weekend approaching. Good luck!