What Causes Delay In Periods,cramps And Breast Tenderness?

Hi, I came off Femulen on 4th March, had a period from 6th March, but have had nothing since. I am now on cycle day 37 and still no period (before when I've been off contraception my cycle was anything between 24 to 31 days but never as long as 37 days) I've been getting strong cramps and very tender breasts (feel like they're burning) for the past 5 days and feel as if I should be on my period, but no bleeding. I have taken 3 pregnancy tests, all negative, the last one being last Wednesday (cycle day 31). Just wondered if this is normal after coming off Femulen as the patient information states that your cycle should return back to normal straight away so a little worried something else may be going on.