If its not anemia then what is it?!

For about 2 nearly 3 years i have been suffering from:
getting weak and tired easily,
random feelings of dizziness,
a lot of headaches,
and i find it a lot harder to concentrate

ive also had sleep problems, but no matter how i change my diet/routine/sleeping pattern, or what medication (such as melatonin or circadin) it never helps (i only ever got the side effects of drowsyness and vivid dreams)

i also have twitches which may be to do with tourettes (my brother has it and he has some ticks, which i seem to have too....i just randomly inhale through my nose suddenly and tense up for a split second.....it doesnt hurt, but its hard to prevent it happening)

after half a year to a year of it starting i went to the doctors to find out what the problem was, and they got me to have a blood test (i went really white and nearly fainted...i dont like needles, but i never feel that bad when it comes to vaccinations) and the doctors said that i dont have anemia

i also feel a million times weaker when i havent had lots of chocolate or when i am on my period....(hence why i thought it might be anemia)

i also thought it may be a thyroid problem....but i dont know

any ideas?
thanks