How Possible for Pregnancy

Leann
How possible is it to get pregnant after having unprotected sex the day before your period, and he ejactulated inside? 
​I had sex Saturday night on the 25th and was supposed to start my period the 26th. My last period was August 23th. My periods have never been regular but since using Glow I've been able to track them well enough to predict them even if Glow is off a few days. I've had to reset my period log 3 times.
​I have symptoms that match early pregnancy, the most common ones, but I've had pregnancy scares before and know pregnancy and period symptoms are often the same. 
​I guess I just need a 3rd party's advice...