No period since September, negative tests.

The last period i had was in September. I have taken multiple home pregnancy tests all have came back negative. Well yesterday I had what I thought was a period but it was super dark and thick not like the periods I normally have. I also had super bad cramping yesterday and I never have cramps, I woke up today and nothing. I'm just curious if this has happened to other people, if I should be worried, or just forget about it because its normal.