Cycle day 66...

So I usually have 29-31 day cycles, never had a “missed” period except for when I was pregnant with my son. I’m now on cycle day 66. My last period was October 15th. I’ve taken TONS of pregnancy tests (all negative) and also had a blood test (negative too). So I officially know I’m not pregnant but just wondering why all of a sudden my cycle is so late!!! How do you deal with having Irregular cycles when trying to conceive? It’s so frustrating! Idk if I should keep testing for pregnancy or start using opks!