I am sorry to hear that you are experiencing this discomfort. I would suggest that you go to see your primary care doctor
who will be able to help you figure out what is going on and also prescribe an appropriate medication to relieve the symptoms.
Most likely, the symptoms you are having are related to strain or spasm in the muscles of your lower back. This is a common problem in otherwise healthy people, especially due to poor posture (sitting at a computer screen all day) or heavy lifting. It typically does respond to rest and stretching exercises, together with anti inflammatory medications for the pain. Make sure to tell your doctor exactly where the pain is, as well as if there are any strange symptoms like numbness
or tingling in your legs, which might suggest a pinched nerve in your back rather than just a strained muscle.
Although it seems unlikely in your case without other symptoms, occasionally a urine infection or a kidney stone will present as pain in the lower back. Tell your doctor if you are having any urine symptoms, like pain with urination or blood in the urine, as that will obviously change the medical treatment of your symptoms quite a bit.