I am 21 wks pregnant and have traces of protein in urine and now I have pain in lower right side of back. Are they related? What could it be?

Hydrate. Usually trace protein in your urine is not significant, especially if your blood pressure is normal. Hydration is encouraged, also sometimes this can be contamination from vaginal discharge. Back pain is common during pregnancy, as long as you have no urinary symptoms such as burning, urgency, your back pain and trace protein in the urine are coincidental. Consult with your OB if your pain worsens.