Weight Gain

Last week the husband and i went to the prenatal appt. and when they checked my weight i was 124lbs. and the week before that i had gotten sick and went to the ER and i weighed at 126lbs. my pre-pregnancy weight was 135lbs and dropped to 119 because of the morning sickness. my midwife wasnt very happy of course, and told me i had to start gaining some pounds. is there any secrets to a healthy weight gain that you ladies might know of. need some expert advice, since this is my 3rd pregnancy. the last 2 were miscarriages...... please and thank you <3