Extreme Fatigue - Help Please?

BreakfastAtCharlottes

Hey everybody,

for the past few weeks, I've been feeling extremely tired all day. I eat around 1600 calories a day (that's including my calories "earned" through working out) and get lots of sleep (9+ hours a night - I've always needed lots of sleep). The only thing I have changed in my workout routine is having moved my workouts to late morning (usually between 10-12) and doing both cardio and weights instead of alternating steady state, HIIT, circuits, etc. I do make sure to eat nutritious foods as well. I aim for 2-3l of water a day.
Any idea what might be wrong? I suppose I could try eating a bit more, but my weight loss is extremely slow as it is, since I have a thyroid problem (hypothyroidism, which means my metabolism is slower).
I would appreciate your advice so much!
Thanks.