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.

Thoughts: Discuss a medical work up to assess what has happened to your metabolism. Eat healthy foods that are high in calories. Eat six meals per day. Work on strength training to build your large muscle groups. Work out with heavier weights with fewer repetitions. Sleep at least 8 to 9 hours per night. Hydrate well with water.