Faint lines but negative blood work😩

Has anyone else experienced this before? I have been getting faint positive pregnancy tests for over a week now but last Friday got a negative blood test with hcg of 3. I am 7 months postpartum and only initially tested because I was having bouts of nausea throughout the day. I have used multiple brands including a medical grade urine test which had a faint positive as well, hell my husband even took one and it was completely negative. I’m still experiencing nausea and other symptoms I remember from my other two children’s pregnancies. Also, my lines are consistently staying pretty faint. HELPPP😩😩