Gosh, you are going through a hard time. You do sound to be having a hormonal issue with the hot flashes and losing massive weight can cause that! I was trying to get pregnant and was about 103 pounds. My doctor made a strong suggestion that I needed to be at a higher weight to have regulated hormones. I was about 115 when I started having regular periods. This is hard stuff. Have you had your thyroid checked? Sometimes an overactive thyroid can cause the symptoms you describe.
If you're of an average height and only weigh 100 lbs., it's not surprising that your periods would stop. If a woman's BMI goes down too far, that is one of the things that happens. No, you haven't "blocked your blood flow," you just don't have enough body fat for your body to allow you to ovulate. It's probably survival response from back when humans were hunter-gatherers -- if there isn't enough food, the body doesn't ovulate because getting pregnant would risk starvation.
I think unless you find a way to gain weight, your body will react in a lot of ways besides hot flashes and lack of a period. While you're working on finding out what is wrong with your stomach, can you at least add some calories through some of the body-weight increasing drinks that they sell?