Does anyone know how long it takes your hcg levels to drop back to normal? It as been 6.5 weeks…

Does anyone know how long it takes your hcg levels to drop back to normal? It as been 6.5 weeks since I had my daughter and I haven't had my period back yet. My boyfriend and I had unprotected sex and I want to know how long I should wait before taking a test without it being a false positive.. I've been FF so that's why I'm concerned. I know usually BF mom's don't get their period.