Period and positive test?!

I had a miscarriage in April and got my period back in may. I took some pregnancy tests in June but then started my period so I took one after it was over to confirm that I had no hcg in my system. It was negative. So we TTC again last month and I had several faint positives but I started my period Saturday (it was due to come today). I have had sore boobs and the frequent urge to pee but I took another test today just to make sure that it was negative and it's still faintly positive. Can anyone help

me understand why it might still show a faint positive if I'm on my period?