Later period, is it too soon to test?

Nancy
Hi girls, I haven't gotten my Period since March 7th. I have an irregular period which usually come between the first or second week of the month but it didn't come at all last month and it hasn't come yet this month . I took a test last week and it was negtive :(. 
I was wondering if anyone had any suggestions as to what pregnancy test to use and when to take it. Thanks in advance!!