What Causes Delay In Periods And Pain In Abdomen And Lower Back?

I have not had a period in 9 months in losing weight fast my tubes are tide and I have pain in my upper and sides of my stomach and my lower back I I m so skinny some days I don t eat at all but most of the time I eat once a day sometimes when I wipe there is a little blood but that s just sometimes I ve had cat scans on my chest and been to the doctor what is wrong with me