How many calories?

So I just got back from the diabetic clinic and they weighed me in at 104.. in January when they weighed me I was 112. Needless to say both my doctor and I are quite shocked and concerned- especially since I haven't had my period in a while.  I'm not anorexic, but I have been restricting for quite some time and am definitely embracing the whole re-feeding process. I have missed all of the delicious foods!

For some info, I'm 5'5" and am 16 and a half.  I go to the gym 3x a week for about 45min-1hr at a time.  Now my question is how many calories should I be consuming a day to reach about 110 by no particular date?

"I'm not anorexic, but I have been restricting for quite some time" strikes me as a bit of an oxymoron, I have to admit. That said, restriction might not specifically mean to very low amounts, so I can see how that might be. Either way, I suggest you do two things: stop exercising as this can contribute to amenorrhoea, and aim for a sedentary minimum of 2500 calories. There's lots of tips for food ideas and how to work this into your day, but a good rule of thumb is to eat six times a day: three meals, three snacks. Make sure a good amount of these come from each food group and make sure to encorporate plenty of fats to help with your period's return.

However, I should tell you now that 110lbs at 5'5 is still underweight. Really, you should be looking at about a 20 BMI to gain to - if your body's set point is lower then it will adjust of its own accord (I recently dropped a couple of pounds moving to maintanance and am now firmly at a healthy weight, but hit a 20 BMI first). This is to help encourage your period to come back and provide a buffer zone from future weight loss and possible relapse.