Give me advice please!

About two weeks ago, I had sex with my friend. He did not have on a condom but he did pull out. We weren't dating or anything, just wanted to have fun. My mother does not know I've been sexually active. I was supposed to start my period 3 days ago and still haven't started. Normally my period is spot on with my <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">period tracker</a>. But sometimes it will occasionally run a day or two late depending on my stress and etc. Should I be worried about me being pregnant? Also, how do I tell me mom I've had sex? When is the right time?