Is there anything to help gain healthy weight?

Okay, so I'm 6ft 125 pounds at the moment because 2 weeks ago I was diagnosed with Mono, which makes you lose up to 10 pounds. My weight is fluctuating between 125 to 126 to 127 because I normally used to weigh around 130-132 pounds. My doctor said I'd gain my weight back and it has been 2 weeks going on 3 and I still weigh like crap.. I also have a fast metabolism and it has always been hard for me to gain weight as it is.
It doesn't matter how many times I stuff my face with food or anything and I just don't gain weight. I'm drinking this stuff called Carnation Breakfast that has a crap ton of vitamins and minerals in it and supposedly it's supposed to make you gain weight and it isn't doing anything for me.
I was curious if there is any healthy drinks or anything out there I can take THAT'S HEALTHY that will help me gain. I'm sick and tired of seeing all these products for obese people to lose weight and nothing for skinny people to gain it.
Thanks.
I was given Ensure Plus at the hospital when I was being watched over with Mono. I did see that it has a lot of protein to help you gain weight.
How many times a day can I drink it?

Lose Weight As You Get Older - Ezine Articles

Recommanded Answer:
Ensure Plus or Boost...Drink them along with meals to gain weight.

• Try protein shakes, get some egg whites , banana or some other fruit, and whey protein powder, 2x a day , when u get up and when u go to bed at night. And if your workin out , your workout routine will depend if your gaining or cutting, go here and u can find lots of free info , as well as great deals on protein powder and other supplements .. http://www.tkqlhce.com/click-7015076-10409415
  Hope this helps
  Good Luck
  R
• The best way to gain weight is not just merely by eating, but pairing an even higher diet with proper exercise and sleep. This is because when you do gain muscle mass, it will help to stabilize your weight. Mainly, the key issue is that your calorie input is not higher than your calorie output, so an increase about 200kcal will not help you gain the weight you need. What you need is a diet that increases your calorie intake by 500kcal each day.
  
  In order to eat a proper high calorie diet, you must make sure that you are eating enough meals rather than eating a lot in a single meal. That means eating as many as 6 meals a day which can be a hard thing to achieve. Nonetheless, what you can do is focus on adding more carbs into your normal meals with more pasta, noodles, rice, biscuits and bread. One little tip I did was to drink 500ml of milk 3 times a day in between my 3 high carb meals to give me the protein I need to gain weight.
  
  As for your sleep, you need to clock the right amount of sleep to stay alert and help repair your muscles. Any negligence will cause your body to burn more calories and destroy hard trained muscle mass. I calculated the amount of sleep by falling asleep and waking up all by myself without the aid of an alarm clock or other distractions.
  
  As for your workout, you need to do a heavy weight workout to get your body used to the stress of gaining weight and help you to gain muscles easily. One way to do that is via the workout at http://gohforth.com. I used it for many years and still stand by it for my clients at the gym.