The issue I have seen is it depends what location you are filing in. In the US it has been straight forward. In other areas local to Thailand they have made the process a bit more complicated adding their own requirements.
The DTV requirements are to prove you have 500k baht. It doesn't say you had to have it for the past week, month, or year. It's in a personal account in your name only and that should be good to go. You can always tell them something like you cashed in some stocks to get the money.
Why are you tray to "prove I am making money"? You have to show money in the bank. Thats the requirement. There is no requirement to prove any level of monthly income.
If you make an appointment at Bangkok Hospital via email they will confirm the appointment in writing. They won't give you a list of treatments and dates until you are seen by a doctor.