Long story short, the doctor diagnosed Beckett with a cold (we were hoping he had something we could give him medication for and be done with it!) and sent us to the ER where a specialist could look at Mackay's hip. He was worried that Mackay had bacterial infection in his joint, which could cause serious problems if not treated immediately.
We got to the ER around 3 pm, waited in the waiting room for maybe an hour for them to take his vitals, then they sent us to a room, where a series of specialists looked at him and took him for tests. Mackay was super brave during the ordeal and even laid still while they took an x-ray of his leg. They were worried that they might need to do surgery to test and reduce the fluid at his hip so they wouldn't let him eat any food despite his endless requests for something to eat. All was well until they decided to put an IV in his arm to do additional blood tests (the results from the blood they took at the doctor's office via his finger wouldn't be back until the next day and they wanted the results right away). Unlike adults where they do an IV on your wrist, on young kids they do it on the opposing side of their elbow and then tape their elbow with a board so they can't bend it. Mackay didn't appreciate this IV AT ALL! After some intense crying, however, he finally feel asleep around 8 pm.
All of the tests indicated that he did NOT have a bacterial infection, but the doctors wanted to monitor him and see how he was doing in the morning. We were able to give Mackay a blessing that night and felt reassured that he would quickly recover.
The next morning Mackay was doing MUCH better and the doctors gave him the okay to go home--horray!!! He played with toys with Beckett and even put weight on his leg. The physical therapist had him do a series of tests and he passed them all with flying colors. He favored his non-hurt leg for about a day but was soon back to his old self. The doctors say he had toxic synovitis, which basically means a virus attacked his hip joint, causing fluid to form around it and the associated arthritic pain.
We were happy Mackay was well and that the only lasting pain was our portion of the medical bills (almost $1k!). Good times...