Progesterone Supplements

Hi ladies! I was hoping someone is going through or has been through this in the past. Yesterday my doctors office called and gave me the results of my second round of bloodwork. The nurse said my hcg had risen beautifully, but my progesterone had dropped some. (I'm 5+5 btw) So she called me in a prescription for prometrium 200mg once a day. She said I could take it orally or vaginally, however I prefer. I've not had any bleeding or anything abnormal, but I'm concerned. Do these supplements generally work pretty quickly to bring that level back up? She said I could come back in next week for another blood draw, but said she didn't really think it was necessary since they work so well, unless I just wanted to for piece of mind and just went ahead and scheduled me for my first u/s at 8 weeks. I'm still just nervous! Any thoughts??