I am thinking about what was wrong with me that caused my m/c. I know that m/c is a common thing but what if something was wrong with me? Then next time I could prevent it

.
My LP is just 10 days. I O on day 20 or 21 of a 30-day cycle. Is that even normal? I read that normal LP usually lasts 12-14 days. Does it mean that something is wrong with my progesterone?
I have another concern about my weight. I'm 5'8'' and I weight 118 pounds. My frame structure is small but I have very heavy bones! According to a healthy weight calculator, i should weight at least from 126 lbs up to 150 lbs. I am trying to gain wait a little bit, but it is so hard

. I gain 2-3 lbs and then I loose them that same day! I feel great, though! I do not feel underweight and I eat every time I'm hungry. My lactovegetarian diet doesn't help with gaining fat either. But, to be fair, I've always been skinny.
So, I have to gain fat just to make sure that my next pregnancy would be healthy. Do you think it is very important to get into "a normal weight' category before pregnancy?