Poor Heartly.
I gather they think it's a sprain, not just soft tissue bruising? With the latter, I've had steroids precribed, which got Jack back to his old self within a day. A sprain takes longer - is he showing any improvement at all yet?
I would definitely voice your concerns to the vet. Last year, just a few weeks after I adopted her, Gracie came back into the house on three legs after I'd let the dogs out. It was late on a Friday afternoon, and I knew I couldn't get her to my preferred vet before their office closed (he's about an hour away), so I took her to the nearby vet I use for more routine matters. I had tried to quickly examine her paw, but it was obvious that it was very painful, so off we went. The vet examined her paw, said she had no cuts or punctures, did x-rays, no broken bones, so diagnosed a sprain and sent us home with an anti inflammatory pain med. I questioned whether he was sure there was no puncture in the paw, because it had certainly seemed to me that it was the paw which was painful. He assured me - no puncture. By Sunday morning, no improvement, and the paw felt hot tgo me, so I gave her injection of antibiotics and Monday morning we were at my preferred vet's office, waiting for them to open. He was on vacation, and we saw another vet in the practice. Gracie had two puncture wounds, and an abcess had formed. The antibiotics started having their effect by that evening, and she started using the leg. Later that week, I noticed that she was having trouble swallowing - back to the vet. They couldn't find anything wrong in her throat, but to me, she was visibly deteriorating even while we were there, so they sent us to the U of I to be scoped. Fortunately, there was a doctor there who had seen cases of tetanus in dogs (most vets will tell you that dogs don't get tetanus), so she was diagnosed almost as soon as we walked through the door. I walked out the door after leaving her in intensive care (where she remained for ten days, with daily visits from me) and having put down a $5,000 deposit. They had never had a dog survive tetanus before - Gracie was their first. It took a couple of months for her to recover fully - I slept on the floor with her, so that I could hold her when her night time muscle spasms threw her body around. The poor dog went through hell.
I had already called the vet who missed the puncture wounds after that Monday morning when the other vet had seen them and put her on antibiotics. I called again and told him about the tetanus. Needless to say, I have never gone back to him.
It also taught me once again a lesson I had already learned earlier - to never, ever, ignore my own instincts when it comes to judging what is wrong with one of my animals.