What Causes Delayed Menstrual Periods While On Metformin?

No period for 7mos. When i stopped taking birth control pills. I took duphaston to induce my period as per my OB advised. Got my period on July 4th til July 9th. I am actually TTC now. I am wondering how long would it take to have my next period. I am also on metformin. Lost 10kilos in 1 month. You think im pregnant? What is the normal cycle should i have? 28days? I am confuse. Because im a bit late. I am already almost a week delayed if i am on a 28days cycle. Please clear my mind...