Can this be leftover HCG?

I’m 7 weeks postpartum. Had sex a day before my 6 week checkup & pretty sure i was ovulating already (egg white cm, temp rise). It’s been 9 days since. My test at 5 days after was 100% negative. Now I’ve been seeing faint lines & todays was more there than the others but idk if it was just line eyes or what because if the other tests had a line, todays should’ve been more visible. Or maybe i had line eyes before & todays was the only one with a shadow of a line??? Or maybe it’s still line eyes. Idk but I’m freaking out. I feel pregnant. I feel nauseous (despite not having nausea much with my son). Super tired (& ive had more sleep last night than in a while). I’ve read you’re super fertile after having a baby so 🤷🏼‍♀️ no need to lecture me either, this baby would be loved & cared for just as much as my first.