Opinions please!

I took my last birth control pill 4 weeks 1 day ago. After my last active pill, I never had a period, and I still haven't. My husband and I had unprotected sex Saturday (today is Wednesday). Starting Monday night, I've been waking up in the middle of the night wide awake. Super unlike me, it's the weirdest kind of insomnia. I've read online that some women have insomnia from the time of conception. Today I had some light cramping and some pinkish (slightly brown) spotting. Could this be implantation bleeding or do you think I could finally just be getting a period?