Missed period on birth control

I've been on the pill since April and it was working great until last month when I got super stressed out to the point that I didn't have a period when I was supposed to. I took a test and the results were negative. I also ran out of packets that month so I stopped in the clinic to pick up some samples (since my doctor wasn't in at the time and just gave me some for free) and now instead of 2 brown pills there are 4 and its throwing me off a bit because I was supposed to get it yesterday but with my old brand I should've gotten it tomorrow. Is there any way to make my periods more predictable? Also, is it bad to take different brands of pills? My last ones were swallowable and the ones I'm currently taking are chewable