why doesn't my bc work right

Ok so I take microgestin and when I stop taking it for the week im supposed to get my period I never get my period. And then like a week and a half later I get it even though I'm taking the pill. I called my doctor about it after being on the pill for 3 months and she said to wait and see if it gets more normal. Its now been five months. But im 17 and my mom just asked if me and my bf are having sex because I told her how the pill wasn't working. And also because I gained weight recently. But I'm not pregnant because I just ended my period like two days ago. It was a freaky experience. Idk: