We are sorry to hear of your miscarriage.
A
miscarriage that takes place within forty days of immersion does not have the same halachic status as childbirth. The
two year exemption from fasting on minor fast days does not, as a rule, apply after a miscarriage within forty days.
Whether you should fast on Asara B'tevet depends on your medical condition. Please check in with your health care provider about the advisability of attempting to fast and get back to us or a local halachic authority with details.