AITA for confronting my girlfriend over soaked underwear?

A little bit of backstory, for the past week we have done nothing but argue, day in day out. She's been finishing late from work everyday and I'd become a little suspicious. It isn't something that normally happens. 

One day I was doing laundry and went into the bathroom after she had come back and picked up socks etc; as I picked up her pants they were wet through. 

I asked jokingly of she'd peed a little to make light of it, but she didn't respond and changed the subject immediately. I asked her out of curiosity and she started shouting saying things like "why don't I trust her" 

Should I have said anything at all or just ignored it? 