Could I be pregnant on birth control?

Ashley • I`m 27,married to my best friend,have a 5 year old and expecting #2 december 2015!!
I'm almost done with my 2nd pack of BC. Instead of taking the placebos I go straight to the next pack so I haven't had a period since I've been on bc. Just a few days ago I started having brown discharge that later went away and I've also been having a few pregnancy symptoms. I was on BC a few years ago and never had spotting so I'm just curious. I plan to take a test soon but was wondering if anyone else has experienced anything similar.