Period weirdness

I was 16 days late on my period, took two pregnancy test, NEGATIVE, and finally came along my period! I have been stressed and then became more stressed about my period not coming and then came down with the flu and I finally started but, I'm coming to the end of my period and in the shower today i was about to get out and I quarter sized blob of blood came out followed by the usual little clots. But, I don't know what that means! everytime I'm really late on my period this happens! What is it? (Lol this has only happened twice and in the past year)