G.K.
With this pregnancy (my 2nd), I've had mild back pain almost since the moment I found out I was pregnant! Exercise has helped immensely! Just in the past couple of weeks, I've been having a lot of tailbone pain, and I have to sit and rest when I feel it because it's usually a sign that I've been doing too much.
As for the stomach cramping, is it your actual stomach like you're nauseous? Or is it more abdominal cramping like you feel before your period? I had stomach cramping in the beginning with this baby because I was so nauseous all the time, and I've had abdominal cramping off and on, especially now that the baby's getting bigger and my tummy's getting bigger.
Sounds normal, but I second talking to your OB if you're really concerned about it :)
I also want to let you know about a great breastfeeding resource called Nursing Mothers Counsel. If you're planning to breastfeed, we're a non-profit group of peer counselors who provide one-on-one support and information to breastfeeding moms at all stages, prenatal through toddler. You can visit our website at http://www.nursingmothers.org, attend one of our breastfeeding classes at Lullaby Lane or Mills Medical Center in San Mateo, and/or call our "hotline" at (650) 327-MILK. Sometimes all breastfeeding moms need is a little support! Have a great day!