I want to know if we are billing the correct cpt/ICD-9 for post partum bleeding.

This is the scenario, Pt has a vaginal delivery or C-section, then get discharged. Four weeks later pt comes back because still bleeding. They do a limited ultrasound 7681526/tc to see what is the problem. NO findings, just hemorrage. Still ok to bill cpt 7681526/TC with Icd-9 666.2X ?
I'm confused because pt is not pregnant anymore. The cpt 76815 is for an ultrasound, pregnant uterus. Please advise.