You can get a iron deficiency blood test done at any General Practitioner (GP) clinic in Singapore for usually about 10-15 dollars. That is probably the most accurate.
If you are quite good with colour, you can try to look at it yourself. People who are anaemic usually look pale as the bedsheet.
And there is an area below the eyelids that we see that it will be pale as well, instead of the usual red. Of course, any usual doctors will be able to diagnose these as well.
Unethical life pro tip (ULPT): If you are willing to. There is another way. Try to donate blood at the blood bank. They might do a simple iron deficiency screening for you before they draw your blood.