I haven't had a period in three months but I am not pregnant, should I be concerned?

August 15th was my last period. I have had 2 children and my periods have been pretty regular up until now. I know I am not pregnant because my husband and I have been separated since June. Some people I talk to say I shouldn't worry and others have me worried that I could be going through early menopause. I just turned 30 so this is very upsetting to even think about. Has anyone else experienced this or have advice to p on. Thanks!! (BTW Yes I did take a pregnancy test once in September and than again two weeks ago, even though I knew I wasn't pregnant)