Took plan b 2 months ago and never got my period, found 3.5cm ovarian cyst on my right ovary. when will i get my period and when will the cyst go away?

Ovarian cyst: Most ovarian cysts of this type will resolve within two months. On occasion a cyst will produce an excess in hormones and will change your period pattern, but only for 1-2 cycles at the most. If you are definitely not pregnant you should return to normal cycling on your own. Remember, emotional stress is a very common reason for missed periods. Your doctor can evaluate this and treat as needed.