Sounds like sciatic nerve pain to me. Very nomal. Try laying on your kept side with a pillow between your legs so one leg is elevated. I prefer my body pillow. Provides temporary relief..
Mostly in my lower back i wouldn't say it's dull but it's not unbearable
Where is the pain and what kind of pain is it?
Upper back pain and tightening could mean respiratory infection.
Lower back pain dominent on one side could mean kidney infection.
Dull over all pain is normal pregnancy pain, growing pain, pain from the extra weight of pregnancy etc