plan b pill


hey all. so I know ultimately to take a pregnancy test if I'm much later, but I need some advice here. I had an incident last month, so I took plan b. I got a period, tracked it in here. all is well. well according to this now I'm three days late for my next period. now obviously I know that it's going to be messed up from taking plan b pill, but how long should I go with no period before I take a test or see a doctor? I was completely regulated before I took the pill and originally get my period around this time anyways. so I don't know if I should be worried or chalk it up to a screwy cycle now.