Not ovulating

I’m only 21 and went to the doctor due to my period missing. She drew blood for my thyroid, and hormones. Everything was normal but my progesterone showed I was not ovulating. She said she was almost positive it was due to my weight, after having my son I gained tons of weight and currently the biggest I’ve ever been. She advised I lose weight and it should start my ovulation/period back on.

She didn’t think an ultrasound was necessary right now, and was almost positive also I didn’t have pcos due to NO other symptoms.

That being said, can no ovulation be due to being very overweight ????