can a doctor tell if your pregnant by looking?

I went to my OB the other day and he didn't do a pelvic exam but he did do some cultures. He then gave me naproxen for my bad cramps and new BC. My period isn't supposed to come until the 16th but I have been having light cramps for the past 2-3 days. He told me to take my naproxen before my period starts but he didn't give me a pregnancy test at my visit. Can he tell by just looking if I was pregnant? I don't want to take these meds if I am pregnant, should I take a test or not worry about it until I start my period?