12 weeks post partum. I have extreme chills. Temp is normal. Feels like my blood is ice cold. Infection?

Could be. Look out for possible sources of an infection: sinus pain, sore throat, productive cough, diarrhea, low pelvic/uterine pain, foul smelling vaginal discharge, breast pain/redness, burning with urination or peeing frequently. Are you around others that are ill? Breastfeeding? If not, you may be just starting to come down with something. Hormone changes, especially thyroid can also do this.
See a doctor . If you feel that bad you should see a doctor for evaluation. Extreme chills warrants a visit.