Low HCG with symptoms?

Melissa
I'm so confused right now ๐Ÿ˜”๐Ÿ˜” 
I had a miscarriage on 9/11-9/17 I completely stopped bleeding and all my symptoms went away. I was 4 weeks according to the US I did on 9/8. 
I'm expecting my period around 10/14 based on my previous cycles and it doesn't come. I test and it was BFN
10/16 I still had no period but my breaths were starting to get sore. Took another test and it's BFP
Went straight to the ER to get everything g checked out and based on the US I'm about 4 weeks with only the ending sac visible. 
But my HCG is only 32.6!!!!
Do you think it could be the sac from 9/11 that I never passed? 
Why would my breasts suddenly swell and hurt if I wasn't pregnant??? 
Anyone have any stories please share ๐ŸŒˆ