I was having sex with my partner, and he came in me, then later that day I start my period, is there still a chance I could be pregnant?
There is always a chance.. But a period is usually a sign that the previously released egg has not joined with the sperm and been implanted in the uterine lining. In other words, the chances that you are OK is pretty high. But in another post you say Planned Parenthhod "hooked you up". Are you on birth control? If so, what does it matter?
Sperm can live in the body for up to five days if it is in female reproductive tract beyond the cervix. Fertilization can occur anytime live sperm meets up with a live egg.