Could Brown Vaginal Bleeding Be Due To Overdose Of Birth Control?

I m on birth control pills, and I missed two doses so I ended up taking three pills on the same day as my doctor had instructed...I think it might have been a day or two after when I started getting cramps and spotting. My period usually starts on Tuesday/Wednesday, but this started on Saturday, three days earlier than I usually start spotting. The blood is also thinner and browner than normal, and has a stronger odor. Is this because of the heavy dose of birth control all at once, or is there something else wrong?