trying for a baby for almost a year now. currently on thyroxine 200mcg-as i have underactive thyroid. missed my period for 4 days now. have severe back and stomach pain. i also feel giddy. i tested if i was pregnant, but recieved negative result. am really upset now. what might be the cause. can i be pregnant, if my hubby and myself are normal and have had all the tests done, which is normal.