Dog limping (back leg)?

My dog is a male 8 year old maltese/pekingese cross. Since last night he has not put his back right leg on the ground when he walks and is limping pretty bad, but his leg doesn't hurt when i touch it (I touched his foot, knee and the rest of his leg and he didn't yelp). This is weird because he was fine in the morning and then the dog groomer picked him up and took him to get his hair cut. I noticed that he was limping after she dropped him off back at my house. I looked at his foot to see if anything was stuck inside it but there's nothing, and he doesn't seem like he's in pain because he hasn't whimpered or anything. I had him lie down in his bed all night but he is still limping. What do you think is wrong with his leg and should we take him to the vet (I'm 15 and I was home alone when I noticed so I couldn't tell my parents)?