hello there.. I hope you have confirmed that you are pregnant by a urine test or blood test as the gestational age of 4weeks 5days cant be seen on ultrasound. Even a transvaginal ultrasound can show pregnancy only after 5weeks. If you havent done your pregnancy test, i advise you to do it as it might be a simple delay in your periods which has now started with brownish spotting. Incase you have done or your pregnancy test comes positive , then you can start progesterone tabs though their efficacy in preventing a miscarriage is not yet proved completely. But there is no harm in taking them either. Bleeding which starts so early in pregnancy may not be a good sign that pregnancy would continue. I suggest you get your ultrasound done around 6weeks to look for the gestational sac with fetal heart and then start progesterone accordingly. Meanwhile you should avoid sexual intercourse, heavy exercise. Start taking folic acid tablet once daily 5mg . Avoid smoking drinking incase you have these addictions.