Feeling constantly tired ...
need to get some test...
Easy fatiguability and persistent tiredness is associated with a few known condition. It could just be lack of sufficient sleep or a low mood / depression. It could also be due to a few medical condition such as diabetes, anemia, hypothyroid state and nutritional deficiency.
Assuming you have no history of depression and your sleep is normal, I will recommend you to get a few tests done. The tests include complete blood count, ESR, blood sugar level, thyroid function test and vitamin D / b12 levels.
Hope this helps. Let me know if you need clarifications.