Spotting at 12x3 weeks??

Ha
I woke up this morning to pee and there was a light pink color when I wiped. And now there is a medium brown discharge, I've also had slight cramping since yesterday and lower back pain that's been there for about a week.
 My pregnancy has been pretty normal and I'm currently taking antibiotics for a UTI... I just had my first OB appointment 4 days ago and an ultrasound. Baby was fine and really active.
Anyone else experience this? I'm just worried 😢