confused, thoughts?

I miscarried early November, was informed November 15 and had d&e; two days later. My period returned December 15th. My husband and I have been using condoms per Dr orders though probably aren't perfect... I spotted for one day mid to late cycle and thought little of it. Our results from the testing came through that the baby had triploidy and to proceed regularly. The Dr also asked me have my beta drawn just in case. The script just came in so I haven't gone yet.

All this said, I should have had my period on Friday. I tested Thursday night with a basic blue test and it was negative. I still haven't gotten my cycle so I tested again this morning, now 4 days late. The second line appears very faint, to my eyes. Am I possibly pregnant again? What do you think? Is it possible? or it possibly just leftover hcg in my system?

thank you in advance.