Should I Be Concerned About Delay In Periods After Switching Birthcontrol Pills?

Hello. I have recently switched from Ortho Tri-Cyclen to a birth control with less estrogen and I am on my fourth week. I spotted for two/three days but now I still have yet to start my period and I start my next set of pills tomorrow. I have never had sex so I know I am not pregnant, but I was wondering if missing a couple pills could throw off my weeks? As well as is it okay to miss a period when switching birth control or should I talk to my doctor?