When should I start to worry

Hey so I'm 16 days late for my period. I am really bad at taking medication but I had been doing really well after being off of it for a month and I took it every day like clockwork. Well I moved right around the time I started a new back and I lost it in the move so I'm not on it now because I was told to start after a period. I was sexually active but we used protection, but I know that can sometimes not be the most effective way. I have never been this late for a period ever when should I start to worry or even take a test?

****UPDATE*****

Took a test and it was negative. I am very thankful for it because I know I am not able to bring a baby into this world right now. My best friend did alot of research about pregnancy and all the different types of options that I could have with no judgement at all as well as what could cause a missed or late period. She also researched the best way to support a friend through a unexpected pregnancy.