Why haven't i had a period?

i had a internal ultra sound 4 weeks ago and have had a lot of pain since i have been to the doctors and they told me i had a water infection and put me on sevraral types of antibiotics since but i was told that i have had a misscarage last week and it was spotted on the ulta sound but i have missed a period and had no bleeding at all and keep getting sharp pains in my womb i have been to the hospital and doctors many times but i dont no why i havent and i am really woried can anyone help me as my doctors are not giving me any straight anwsers