Hi there
I am not sure what kind of universities you received the interviews from? But, as far as my experiences, if they do not mention anything after a while ( such as 2 weeks, a month or more). It means that they are not interested in your case. I know this is weird but the truth is they do not mind sending a interviewed candidate a goodbye word. I say so because I used to have the same situation like yours. My advice is sending them a nice email saying that you are waiting the response from the interviewer, then do not care about it and start to find another chances for yourself.
Good luck