9 days late

My cycles are always on time every month sometimes a day or two late but this month I haven't come on my period and it's bn 9 maybe 10 days late. I have done probably 5 pregnancy tests and they are all negative. Why am I late? It doesn't make any sense, I get the odd cramp and back pain but that's about it. Normally when I'm pregnant it will show quite early on in my cycle which has happened both times in my previous pregnancies but this time I'm just confused. Can anyone please advice ?