Late Period?

My period is late by four days. I just recently started a new job and came back from seeing my uncle who is diagnosed with ALS. So it was a stressful and emotional week and my period was suppose to start May 31. My cycles are usually 30 days long and my boyfriend and I had safe sex May 9th with condom. I have taken pregnancy test twice and all came back negative. Try to induce the period with honey and warm water and parsley tea. Nothing happen. Trying the vit. C method to see if that works. Is my period late just due to stress? I have a history of not having a period for two months. Please relieve my of my anxiety.