What Can Cause Delay In Period?

thanks in advance... my hemoglobin level is 9.5 and I am late on my period (second time in a row now) - 10 days late... I also have weird pregnancy symptoms (i am not) like breast tenderness and waking up at 5 pm... I am 40, have 2 children and also on methamozol 2.5 mg (for thyroid balance, which is now for 3 months is normal)...