Bleeding after plan B?

Hey ladies- I made a mistake and had unprotected sex on the last day of my period. I took plan B 30 hours later and now it has been 5 days and I’ve started bleeding a brown-tinged blood (not spotting like filling a tampon in 4 hours type blood). I also have been feeling extremely weak and my stomach has been hurting to the point where I can’t sleep well. Is this normal, or should I consider seeing a doctor?