Worried I might be pregnant..

So I had sex twice on the 4th and once on the 5th. He pulled out. I’m on BC but always forget to take at the same time each day. I started spotting yesterday a little and today. Not much at all just enough to wipe. I’ve had back pain and mild cramps. My period isn’t due till the 28th and my fertile window started the 11th. I just didn’t know if it could be possible?! And when to test?!