Bleeding on BC

So I’ve been on birth control since March, and I’ve never experienced any mid-cycle bleeding before either on the pill or before. I’ve never missed a pill and take it between 10 and 12 every night. I also have unprotected sex with my boyfriend. Last night I had a bit of left-sided pelvic pain, but it didn’t last too long and was more of a quick, stabbing pain. This morning, after going to the bathroom I saw a bit of blood. Most of it was brownish, but there was a bit of reddish-pink as well. I’m about halfway through my pill pack, so I shouldn’t be experiencing any withdrawal bleeding. I was wondering if anyone had any idea what this could be or if you’ve experienced anything similar!