What's going on?

Ok I'll put this short. I've been lifting weights 5 days a week, starting about 5 weeks ago. I have a 3.5 month old baby who is ebf, and I still got my period about 6 weeks after she was born, and it was regular. But now, I am on cycle day 35 and no period, and negative pregnancy test. Could lifting weights change my cycle? There's absolutely no sign of my period coming, it's 4 days late. (I have a longer cycle average of 30 days) I'm so confused.