6dpo positive blood test?

I have to go get a blood test today for pregnancy for an upcoming surgery next week. Normally I would 100% not think I would be pregnant. We have two children, one still breastfeeding constantly but just got my period back this month. My husband just had his vasectomy a month and a half ago. We had sex the weekend after my period stopped and after the fact realized if my period go back to my old cycle which were very short I could've very well ovulated and could be pregnant. My surgery is for pain in my uterus so not sure if all my symptoms are related to that or if I am pregnant. I definitely feel like I could be but you never know when your hormones are out of whack. Just wondering if anyone else ever got a positive blood test at 6dpo, definitely don't want to have this surgery and they won't do it if I am pregnant but will it show up this early on a blood test? Or could I be pregnant and it not show up and I end up going through surgery anyways.... Thanks ladies!