every day or so for the last 2 weeks approx my 11 month old staffordshire/collie cross has had these coughing fits.it sounds deep,VERY chesty,but not wet and no mucus comes up,then he gags and it seems like he's getting sick but nothing comes up and then starts again,it can go on for a while but he seems happy enough,i usually rub his back like a rough massage with both hands for about 3 minutes and it stops,sometimes it starts again and sometimes he's fine,it's really strange,is this kennel cough?he hasn't been in a kennel and is only around other dogs when i walk him....should i bring him to the vet or do you think this will pass?