Thickened endometrial lining

Hi

After an ultrasound scan, I have been told that my endometrium measures 5.7mm. Due to this I have been referred to gynaecology and am worried sick. 

I am also worried about the tests and how painful they may be. I am post menopausal and only presented due to a bacterial vaginal infection that has now cleared with antibiotics. 

Has anyone had anything similar or can tell me what to expect?

Thank you