This is so interesting! I'm in an almost identical situation as you Mamabean.
I'm 8+ 5 by LMP, 6th pregnancy, but 5th child (had an MC in June). I too got an early BFP, I'm massively bloated (although that's not unusual for me in pregnancy) & I was sure it was twins. I just 'knew'!
I had a scan last week at 6+5) & there was a sac with a heartbeat & something else!! I had an internal scan too & there was definitely only one heart beat, the sonographer thinks the something else is/was a collapsed sac. It was smaller than the sac with the heartbeat & a different shape. Perhaps that's what your other 'thing' was?
At first I kept thinking (maybe hoping
)that when I go for my 12 week scan there'll be another healthy heart beating away, but now I think I know that's not very likely
Good luck
I will be checking back to find out what happens with you scan x