I doubt they will be interested in any short trips you do to other countries, either for work or pleasure. Your DTV, once approved, is activated on your first arrival in Thailand. There is a time frame stated in the application process which you should have given information on when you are planning to travel to Thailand once your DTV is approved. I don't think you need to worry. 😊

Go and make an appointment with a doctor here whilst you are in Thailand and explain your medical situation and what you are hoping to put in place for ongoing monitoring/treatment for your condition. They will either refer you to a suitable consultant or make a treatment plan for you at the clinic. You will need a letter from the GP or consultant (headed paper) saying you have been appraised and that you will be returning to Thailand to treat an ongoing condition. In addition to that, make some provisional appointments for treatment for roughly when you intend to return (I made 12 over a three month period, one per week) and have the clinic print them out for you on headed paper. I applied through the UK Embassy whilst I was home in the UK and got my DVT approved about 14 days after I submitted all the documents. Hope that helps. Good luck. 😊