Lost 11 pounds in my third trimester in a month what could be wrong ?

A mistake.: It is unusual to lose weight late in pregnancy. The most likely cause is a mistake during "weigh in". If not, then you should talk to your doctor about and possible pregnancy complications like new onset of overt diabetes, hiv, tuberculosis, or other serious medical condition, in which case you would almost certainly be having symptoms.

Weight loss: Are you eating healthy? Drinking plenty of water? Weight loss is not a good thing in the last third of pregnancy. Maybe an added energy drink, like boost or ensure, might help. Speak with your doctor.