Why do I all of a sudden have an acne problem?

I've always had good skin in the past and I didn't get pimples that often. Then I was on birth control (the patch, then I switched to Yasmin the last couple months) for about a year and a half and birth control is known to treat acne, so I had virtually no pimples at all during that time. Now that I've stopped my birth control, just recently I started getting more pimples than before I even started birth control. I have about 4 on my face right now. Before I would never have more than 1 at a time. What's the deal? Are my hormones out of whack still?