Pregnant even though I’m on the pill?

I had my daughter a year ago and have been on birth control since. Her father and I split up and I just recently had sex for the first time since then. I found out after that the medication I’m on for depression, which was just changed right before I had started having sexual again, might cancel out my birth control. The way it was explained to me is that it all depends on the user’s hormone levels. I have a major hormone imbalance. I’m scared that there’s a chance I might be pregnant.

Because of my hormone imbalance, I had symptoms almost immediately with my daughter. I’m talking days after conception. Well the last several days I’ve had bad nausea and fatigue. I’ve thrown up a couple times and my boobs have started hurting like crazy again. The sore breasts I didn’t read into too much because I’m still nursing my daughter. But the rest is very out of character for me.

Anyone ever been in a similar situation? Or have any advice about how to handle the situation?