I've had 2 c-sections, and I'm a runner. I have had lower back pain and hip flexor pain. Stretching and time off running don't help. Help?!?

Time to see the doc. A sports med doc can help you with this issue. A thorough history and exam coupled with x-rays and potentially other forms of imaging will help confirm or exclude the causes. In your case, a running gait and postural analysis plus strengthening exercises may be quite helpful.
See sports medicine. If self management is not working, i suggest you see a sports medicine specialist for a good assessment. Many things might cause your type of problem. Get help.