My doctor ordered a second mammogram and it's still not clear if anything is wrong. What's next?

Second mammo. Difficult to speculate without details, but possibly additional imaging such as ultrasound or breast mri if the mammography workup is ambiguous.
Continued workup. The first step to screening for breast cancer is a screening mammogram. Many times more images are needed. This is called a diagnostic mammogram. If it is still unclear the next step is a breast sonogram or a breast MRI and evaluation by an experienced breast surgeon.
Well a more focused. Exam with magnification pictures means the doctor saw or felt something that required a closer look.