Low Progesterone/ NFP

Emily
Hello! This is my first post - I am pregnant after an early loss at the beginning of September. Our due date is July 20! We are so excited, but taking it one day at a time  for now until our first appointment and ultrasound (Thursday 12/3).
My husband and I practice Natural Family Planning (Creighton Model) and through this discovered that I have low progesterone. Doctor put me on supplemental pills (200 mg) Peak+3 through P+12 last June; when we became pregnant she doubled my first to twice a day, everyday. Now, she had prescribed progesterone in oil injections. Is anyone familiar with these in this context? My husband and I are a little uneasy about the application, accuracy,  effectiveness and so on. I am assuming injections are more affective than capsules? Just looking for someone going through something similar...