Surgery and Periods?

So last month my gallbladder like had a mental breakdown and started falling apart. Well my surgery wasn't scheduled for another month so I thought I could just push through it and that wasn't a good idea. So like after a few days my fiancé makes me go to the ER, April 11th. They of course admit me. Tell me I need emergency surgery but also that my liver was freaking out too and I had pancreatitis, all because my gallbladder was being a bitch so they couldn't do the surgery to remove my gallbladder till they brought my levels down. Well they did the surgery the 16th and told me the infection was so bad that if I had waited any longer it could have killed me. Cool. Anyway, my last period was April 4-8th and I'm 10 days late. And my fiancé and I have only had sex once and I couldn't even let him finish because of my surgical wounds hurting so bad. So can stress of surgery really fuck up your system that bad? Or is my body turning against me and just getting itself pregnant without my permission? I should note that I took a pregnancy test yesterday and it was el negativo.