Don't think you'd have symptoms that early.
Not pregnant. If you got your period after sex, it's cleansing the uterus. You would have to have sex have you're done with your period, like day 10-14. That's when your egg drops
Symptoms won't be this early.. also. You conceive 2 weeks after your lmp. If you started your period. Your fine. Light or not. Only way to find out is a pregnancy test taken the day your period is missed, and 4 weeks after your last period. Good luck