What has helped me immeasurably is MORE exercise, not less. And the right kind, obviously. I feel so much better - ie move briskly with no pain - after my yoga class. To go through the week in between yoga, I do:
1.pelvic rocks before going to bed (relieves pelvic/abdominal pressure because the uterus just hangs loose)
2. squat a lot (stretches perineum area to prepare for birth)
3. kegels to avoid incontinence and feeling as if the baby is about to drop out
I dislike swimming personally, but know it is also greatly recommended to relieve pelvic pressure.