It really depends what those risky things are. I mean, are we talking about unprotected intercourse with withdrawal? That would have a significantly higher risk than, say, mutual masturbation.
You can check this page for more: What's The Risk? - Five Easy Pregnancy Risk Assessment Flow Charts
What you need to know is that sperm can live for 7 days in a friendly environment--like the vagina. So, having gotten your period, you aren't likely to be pregnant, but any time you've had unprotected contact there is a risk.
You and your partner are also at risk, by doing "risky" things, for STD/STI transmission, and both of you will need testing. See Testing, Testing… for details.
And - so that you don't have to worry about this in future - check out Safe, Sound & Sexy – A Safer Sex How-To.
Kissing girls in English at the back of the stairs, you're a honey with a following of innocent boys, they never know it because you never show it..." - Belle and Sebastian