Ladies need your advice please! Thank you!

So i got my bfp finally after a year of trying for our rainbow. I ovulated late either on the 20th or 21 of sept. The 28th of sept late that night i noticed very faintly a bit of brown spotting then from there all the way til about Saturday i had lots of cramping light brown spotting, it felt like my period was coming but nothing showed. So Saturday night around 11pm i decided to take a test cause i had a small wave of nausea and it came out positive. Fairly dark too. I started noticing the spotting came back on either monday or Tuesday very light. I called my obgyn and she had me come in for an early scan and blood work ( due to me having pcos) she prescribed me progesterone and advised me to continue the metformin. When they did the scan they couldn't find a gestational sac. She said i was very early in the pregnancy about 4w due to ovulating late cause my last cycle was on aug 28 but she was going to monitor me to make sure i didnt have a tubal pregnancy.. the spotting stopped and my hcg doubled from Tuesday being 300 something to Thursday being 600 or 700 cant remember what they said. I noticed when i woke up yetserday morning (Saturday) that the brown spotting started up again. Very light. Then it finally stopped. Ladies what could this be? So nervous about a tubal/miscarriage . Last pregnancy i miscarried at 11w only measuring at 5w empty gestational sac. Had no symptoms really. No spotting either. I know every pregnancy is different. Could it have been that it was to early to find anything??