well if your blood was brown or brown and red and your having cramping then it can be that your preg and if you miss a pill you have more of a chance of getting preg,,so if i were you i would take a test a blood test
If you "missed some pills" it can cause all the things you describe, including pregnancy if you're not careful. Get back on your pill schedule and use extra protection until you've maintained that schedule for the next month. They're serious when they tell you not to miss any pills.