What next?

Last summer (July) I had a MC at 12 weeks. After having a D&C;, my body didn't seem to be going back to a normal cycle and I was having a ton of physical and emotional issues. Ended up consulting with a different OB and found out that my HCG was still elevated in December! It was like I was pregnant the whole time because there were retained "products of conception". Had another D&C; at the End of December and finally was back to a regular cycle. At the end of March, I found out that we were again pregnant, unexpectedly! Within 2 days, I was no longer pregnant. We decided to not try for a few more months (since I had also just started a new job!) Fast forward to November and we decided it was time. I used 3 apps, tracked everything, used OPKs, my husband would take my temp when he woke up... and it worked! BFP! But sadly, it again only lasted for 4 days. I tracked last month and I don't even think I ovulated. At the end of the month, just before AF was due, I went to see my doc. He did bunch of blood tests on me and one on my DH and we found out today that they all came back normal. So what do we do now? Keep trying? I'm 36. My DH is 35. We have a 4yo daughter who we had no trouble getting pregnant with. But I have had an ectopic (2 years before her) and now 3 MCs. I'm not ready to give up but so anxious about getting a BFP and having another MC!