Stephen should just have a button that he hits to send out the standard reply because it's alway spot on - I would add to his response: "what are your goals?".
I don't personally think 3-5km is long. I think 7-8 miles is starting to be long. Admittedly the last time I did any running in Thailand I thought I was going to die.
Based on knowing absolutely nothing why not experiment by doing a long run at weekends? Build it gradually. I know there are running clubs in Bangkok that you could hook up with. Where abouts in Thailand are you?
Alternatively, if you need to run for a test or a race then run more. Loads of posts across the internet about an upcoming 2 mile test that will make or break a career and can the poster just bench 5 days a week + a lap of the track with a weighted vest. Sure you can.