If you track your BBT and are truly late, then how many DPO are you?
If you don't chart your BBT and therefore don't know if or when you ovulated, then you should test once a week until you either get a positive HPT, your period, or hit CD60, at which time you should call your doctor to discuss jump starting your cycle.
It doesn't matter how 'regular' you were in the past. Any one can be 'regular' and then one cycle turns a little wonky. If the pregnancy tests are negative, then (for now) you aren't pregnant.