I missed my pill & have a question

I was on the 2nd week of my pill pack and I missed one of my pills (I dropped it on the ground outside  so I didn't want to take it). The next day I took my pill at the correct time but I started cramping and I had brown discharge and the following days I eventually started my period. This past Sunday was the last day of my pill pack and I haven't started my period, am I supposed to have it again ? Is it okay to still have sex on my placebo week since I missed that pill a week and a half ago? Also Ever since I missed my pill(a week and a half ago)  I have been taking my pill on Time and haven't missed one. & I've been on the pill for about 3 months now. I just want to make sure I'm safe from getting pregnant. Also is it normal to start your period early if you miss a pill?