How much should I be eating?

Penny
It occurred to me yesterday that I'd rated u see 1000 calories and I'm 13 weeks pregnant. I know not good. But then when planning dinner discovered that dinner alone was high in calories, yet still under the 2000 calorie normal diet. 
I am over weight, and pregnant, and obviously I don't need to gain weight, but I would like to start maintaining or not be loosing as much. How many calories should I be consuming??? 
I've heard you should only eat about 300 calories more a day, so that's 2300 a day, for normal ppl. 
But on a bad day I'll eat as little as 600 calories, on a good day over 1200, but less than 2000, so...what should be my goal?