Super tmi pic!

The day after my period ended I had unprotected sex, it last like 5 minutes and then I sucked it off until he came in my mouth (so sorry for the tmi) and the app says this past week is my fertile week and last night I have protected sex but he finished in my mouth...I have had a lot of clear watery discharge the past week which has let me know I’m fertile & healthy (not pregnant) and I see this faint spot in my underwear, what could this be?