Switching brands

So I recently switched brand names of the birth control I was on, December was my first month on them and the last since we wanted to TTC in the New Year. We had sex 3 days during my ovulation window, is it possible I could have conceived in December from switching brands? I had dark but light bleeding from 25th-29th. Ever since I was supposed to start taking them again and haven't I've had mild cramping, bloating(almost like butterflies), back pain, and pain on my left side pelvic area. Opinions, suggestions, anything?