What year are you? I didn't go to lectures during MS1-2 so my time was largely my own and I was able to pretty easily schedule my time around the needs of my pup. Taking the time to really train a puppy is worth it, but it is VERY time consuming if you are going to do it the right way. If you are an MS1 currently then by the time you get to clinical years your dog won't be a puppy anymore which makes things a little bit easier, but there are still some obstacles to overcome. In my opinion, it's not fair for a dog to stay home alone all day while you are on a 12hr shift (let alone when you have to take 24 or 30hr call) and so if you don't have friends who can help out or are not able to pay to send your pup to doggie daycare, don't do it.
I also second what was said about looking into the cost of vet care, emergencies, food, toys, etc... Also consider if you think having a dog will become an issue when/if you have to move for residency, etc... I definitely understand the desire to have a dog, I love my dog like he's my family. But they are a lot of work and can cost a decent chunk of change to take care of, so just make sure you are really ready to take on that commitment before making any rash decisions.