I have had lower back pain (right above my backside) ever since I had my son. What can help?

I was told I had "back labor". One doctor said it was sciatica and another posterior pelvic pain. All I know for sure is that my son is 19 months old and I still am in pain... The pain gets worse after a day of lifting my son over and over again. Anyone else had this problem? If so, what helped you? Thank you!