Boots on the Ground, you really do need a bike fit as a first step, also just saw Gary's comment which I agree with entirely on improving your core strength, and then if the pain continues after that it's impossible to give advice without an accurate diagnosis first. I am a sports medicine doctor so you can trust me on this, especially for low back pain which is very complex.
Ask your doctor for a referral to a physical therapist. These people are really better than most family docs, and myself included, at determining exactly what structures are inflamed and causing the pain. They are marvelous at detecting muscle imbalances, tight joints like hip flexor tightness, or lumbar spine degenerative changes. Basically they will ask you to point to where it hurts, what makes it hurt, and take it from there to come to a diagnosis.
Always go to the best. Check around in your town for a sports oriented physical therapist or get feedback on who is the best PT in town. Talented PT's are amazingly effective, non-talented ones can missed diagnosis entirely. They will design a completely natural strengthening/stretching program that takes a few minutes a day that should be continued for the rest of your life to get rid of the pain and keep it from leading to degenerative changes as you age. Many family doctors just don't know this stuff well enough to give you an accurate diagnosis and will just recommend an anti-inflammatory medication which simply blocks the pain. That's generally not the answer to the problem. It's well worth it, even if you have to wait several months to get in and see the best person.
Let me emphasize a most important physiological principle: what actually stimulates healing of musculoskeletal injuries/inflammation in the human body? Most athletes do not understand this. Passive therapies do not, and they include almost everything: total rest, ice/heat, anti-inflammatory/pain meds, braces/wraps/supports, and then the heavy hitters, chiropractic adjustment, acupuncture, acupressure, massage therapy. Don't get me wrong, these things can all help with the pain temporarily but they do not actually stimulate healing of specific musculoskeletal injuries in the human body. Only active therapy will do this, because it stimulates your nervous system to actually initiate the strengthening process. This means resistance exercises (weightlifting/calisthenics) at home or in the gym. However, for some problems you have to avoid some specific resistance exercises or they can make it worse. That's where the skill of the PT comes in.
Try to remember this principle because in general you are supposed to hit the resistance exercises 48 hours after any musculoskeletal injury unless it is a more severe injury such as a dislocated joint which requires longer rest. Waiting longer than this just delays recovery for most minor injuries.
Hope this helps.
