Why does my underwear smell like Pee?

I'm only 6 1/2 weeks, and I don't think I've lost control of my bladder at all. I showered this morning, put on clean underwear, of course, and when I went to the bathroom two hours later, I noticed that my underwear smelled really bad. It smelled like I had peed several times without wiping, but of course that wasn't the case. Am I incontinent of urine and don't know it? Does that happen this early on?