Pls discontinue the medicine.
Progestetone has a possible complication called DVT which can cause chest pain. Though this complication is very rare but u should not take any chance. If chest pain still persist pls visit a hospital urgently for further investigation and treatment of chest pain.
Next Steps
U can take antacid like Rantac or Pantop now. And stop Miprogen SR. If its due to gas antacid will give u relief.
And once u stop miprogen SR u might get period within a week. Not to worry for that.