Should I be concerned?

I'm not a very big girl 5'4" and my weight 2 months ago was 113lbs. I don't execise and all I eat is junk food pretty much since college started. A couple of friends were telling me that it looks like I've dropped weight and seemed pale. I figured I was pale due to my make up. I didn't believe because I don't feel like I've lost any weight and I figured my boyfriend would notice. I made a bet that I didn't and weighed myself in front of them.  I'm now 95lbs. Now I'm concerned should I go to a doctor? Does anyone know what might cause that?