Different things work for different people (e.g. Heat, cold, stretching, baths, etc.). I've heard that alternating is good but just see what works for you.
A bath often helps me. If it's the baby, try getting baby to adjust position. Get on all fours or lay on your side for a few minutes. Also you can try a support band for lifting up your belly a bit. That helps with sciatica.
Re: What's better for lower back pain?