You need to be taking in about 1800-2200 (or more) calories each day while BF'ing. Taking in less than 1500-1800 calories each day may put your milk supply at risk.
When you were PG your body put extra weight on you that it will now use to make milk...you can lose weight while still eating healthy while BF'ing. I lost lots of weight while I BF both my kids...one for 6mnths the other for 11mnths

HTH