Periods seem odd

I have always been very regular and very heavy with painful cramps on the first day. Since we started TTC the second month my period was alil late and more like a regular period, no cramps either and the third month it was early, again a medium period with no cramps. Dr said things looked normal and I had CF that wld lead me to believe i ovulated...I'm just worried something if off and will keep me from getting pregnant! Any advice?