I can't seem to gain weight no matter what I do. I was a size 5 before my first child and now after my second I am a 1/0 and still thining. Any ideas?

Seek help from a pro. Need to see a physician for an endocrine and metabolic work-up! sometimes pregnancy results in hyperactivity of the thyroid gland. Although rare (about 1/2000 of pregnancies), this accounts for 95% of new cases of newly diagnosed hyperthyroidism. If so you would have a hdd time with weight gain. A blood test for your thyroid hormones, the pituitary gland(tsh). Are necessary to confirm.