Not getting period

I started the pill 6 months ago and in that 6 month period I’ve had my period once (bled) every other month I’ve got all the symptoms but no actual bleeding. I spoke to my doctor and they did an ultrasound and she said I don’t have a thick enough lining as the pill is doing this. So hence why I am not bleeding, she also told me not to be concerned. Is anyone else experiencing this? I make sure I always take my pill the same and I always take the sugar tablets.