I found a bulge in my dogs spine?

My dog is about 3 yrs old and is a border collie lab mix. The past few days Ive noticed a small part of his spine is protruding upwards. Ive had him since he was just a few months and I don't remember his spine feeling like that. He is a healthy weight so I don't think that would be the problem. Anyone have an incite on this issue. Thanks in advance for your help!