period worries

this is somewhat weird but I'm very very scared at the moment . I thought I started on July 11th but instead it was the old brown looking blood but later that day it was a mixture of the brown blood and the new period blood . I waited a few days to see if that would go away and my actual period would come and for about three days , it was the brown blood and a little bit of the new blood . well my full period never came and the mixture between the bloods stopped and my period never came and I'm kinda scared because in the process of that , me and my boyfriend had sex in the shower .. show I be that worried about being pregnant ?