It's unlikely since it's been four periods. By now, a test should pick it up. You should definitely discuss with your doctor as you shouldn't be missing periods unless you're taking the pill continuously without a placebo week.
I have taken four home pregnancy tests and they were all negative. Is there still a possibility?
Is there a possibility of pregnancy? I know with Microgestin, it says if you miss two periods, you should test.
I would talk to your doctor if this is not a possibility.