how low does my hcg level have to be in order to get my period?

i had a miscarriage on 8/02,my husband anf i are not using protection right at this moment. on 8/27 my period came down and on 8/28 i had my hcg level checked again the nurse told me that my hgc level was 635. my period wasnt excacly regular for those couples of days it was on and off. i want to know is it normal to have my hcg so high while having my period? the nurse told me i have to go back in a week to check it again if is still high then shell do more test. please help… im confused…