Spotting for a month after plan B

Tiegan • 18 • Welsh • Jorge ♡ 10/01/2016 •
I took Plan B on the 25th January and ever since then I've been spotting about once a day . Is this normal? I'm on the pill and I had a pregnancy test and it's negative. I've also had a UTI and been on antibiotics so not sure if that would cause me to spot?