I am a 30yr old woman (not ashamed to admit it), have been underweight all my life. I know it's a problem that most wish they had, but really I hate looking like an ethiopian or a crackhead(as I say). After my baby I looked great, kept the weight for about 2yrs... then I got the flu. I lost 18 lbs in those two weeks.
I know part of the problem is my eating habits. I munch all day... no real meals, or maybe 1 a day. My doc told me to start eating 5 meals a day, drinking 2 weight gain shakes a day along with 2 snacks a day. I just can't do it! I don't get hungry and forget to eat, or have to many things going to stop and think about it. I stick to it for a couple of days, then I forget again and go right back to normal. I am about 20 lbs underweight.
I have only gained 2 lbs in 3.5 weeks. Any suggestions?

Your doctor gave you perfect advice. Its hard to switch your eating habits so you have to make a real effort at it. Just like there is no quick fix for losing weight the same goes for gaining weight. In order for any change in weight to be safe it must be done slowly.

If you have a cell phone set it to go off as a reminder every few hours. Then when the phone goes off you know its time to eat. When I first started working out with a trainer she wanted me to eat 5 times a day to help my metabolism and I couldn't get into it. I actually wrote a note and stuck it on my computer at work and it listed times and I wrote EAT next to each of the times. It helped and after about a week it became second nature.

If you don't like being skinny and you aren't much of a eater then eat foods with carbs. I wouldn't recommend eating greasy (every day atleast) foods packed with fat leading to high blood pressure but if you want to gain weight it wouldn't hurt to get 2 burgers from Rally's for $3 or some of their fries (I say Rally's because they are the best tasting).