Can skipping placebo pills cause spotting?


I've been back on the pill for a good 6 months now, or so, and I've been skipping the fourth week to prevent my period. About a month ago I had missed a day and took it as soon as I realized (which was like a day later) with the pill for that day as well. Shortly after I bled and cramped as if I had a period but usually when I'd miss a pill and bleed it was only for maybe five days max, but this time it's lasted for about 3 weeks, but for a good two weeks it's been mostly dark heavy spotting. I don't understand, I've been very consistent with my pills since then. Any input is greatly appreciated. Thanks!