5 weeks 3 days delayed but not pregnant?

Hi nag try ulit akong mag pt and negative. Nagpunta ko sa ob ko and she said na im pregnant and i just need to repeat it again her basis is my mestruation since im regular and was never delayed even once. She also requested an ultrasoubd and the sonologist said im not pregnant ? with thickened lining and corpus luteum. sino papaniwalaan ko