Hihi, I have experienced something similar but not entirely the same as you so I’ll just share my experience. At my week 6 scan (at kkh) my ultrasound technician spotted ‘something that looked like a 2nd sac’ that was empty. My 1st sac had yolk and fetal pole so heartbeat was detected. At week 7 I went to my private gynae and she couldn’t find the empty sac anymore but baby’s heartbeat is detected and growing well. I had brown discharge on and off during week 5-6. So I think your doctor is right in saying that there might be spotting from the empty sac trying to release itself as I believe that was what happened to me.
Because of my brown discharge, my doctor prescribed me progesterone oral medication to be taken 3 times daily until 12 weeks. I’m guessing from the name (Progesta) it could be something similar but you need to confirm with your doctor. What I am taking is actually progesterone tablets which is actually hormones that will supplement the baby and prevent miscarriage. These pills are taken by women with threatened miscarriage as well so it is very safe. I am in week 13 now and baby is growing well. 😊 Hope this helps.