Weird Situation

I had my last period February 22-27. I started taking my new birth control on March 3 (Norethindrone). We used condoms for a week after me starting the bc. Due to a reaction to the BC that caused me to get hives, i immediately stopped taking it when i found out that was the cause. Stopped taking the BC on March 18th. Lightly spotted some brown discharge on March 21-22. Have not received my period yet. Took a pregnancy test that was negative. Should I be worried that I may be pregnant, or could this just be caused from the birth control. I do have a Drs appointment on the 18th - the soonest they could get me in.

I also took the birth control late a couple times. Once by 1 hr, another by 30 mins. We were not using any back up method during this time.

The app predicted my ovulation date to be March 16th & my fertile period to be March 11-17. I had sex with no other forms of birth control on March 16, 17, & 18.