What does it mean?

I had my son on Jan 14. Stopped bleeding around Feb 11 give or take. Haven't bled since then. Husband never really got off in me but said there was a chance for precum. Had a faint positive around March 24. Started spotting that week but the blood was pink/ red and only when I wiped. Went to my OB's office today and they done an ultrasound. They said if i was then i wouldn't be far along so not to worry. Well they couldnt see a baby/sac but said that I was thick. And done some labs. What does this mean?