Hii , Welcome To HCM & Thanks For Asking Your Query Here ultra sound cant clearly determine pregnancy at 3-5 weeks and u need to wait at least 2 more weeks to make it clear but as you have blood pregnancy test after 3 weeks of missing period and it came back negative , chances of pregnancy is pretty less at the age of 46 years it is possible that u might be going through menopause apart from this your problem may be related to many other medical conditions including a uterine fibroid But it needs thorough medical check up and investigations to spot a confirm Diagnosis so i would strongly suggest you to see a Gynecologist to rule out any underlying medical condition I hope it help Thanks & Get well Soon