I'm so sorry for your loss.
I had an ectopic as well. I had 2 shots of methotrexate, but no D&C. I am wondering the exact same thing you are. My Dr. told me 2% of women have had an ectopic pregnancy for no reason. He just keeps telling me there is no reason. My HCG levels never got above 404 either and I was 6 weeks along according to my LMP. Doc said that I can start trying again once my HCG is back to 0, but all the literature and information on the internet says wait 12 weeks. I don't know what my HCG levels are at right now, but I have an appointment next Thurs, and they take blood every 4 days since Friday.
How are you feeling? I hate to see anyone go through this. If you need to talk, or complain, or POST IN ALL CAPS, please do! I sure did last week....!