questions on weight gain?

Wow so this is my first forum post! I'm scared! So I've been using myfitnesspal since late May and have done awesome. I've lost about 70lbs so far, I have about another 35 to go but I've hit a wall. I was doing good, losing 1-2lbs a week and then suddenly I gained! Nothing crazy just a couple of pounds but it's been at least 3 weeks and I can't shake them. I got a fitbit for Christmas and I love this little toy, but it's telling me I should be eating 2-3000 cals a day (depending if I go to the gym). Is this for real? I have a fairly active job, certainly not rigorous and I try to go the gym 3 times a week where I burn approximately 5-600 cals. But in all honestly I have weeks I don't go at all. I'm taking in about 1500 cals now, am I storing fat? Should I be upping my intake? The only other cause I've been seeing for a weight gain is lack of sleep. Now I don't sleep much maybe 3-5 hours a day. I work midnights, have small children, I haven't slept 8 hours in YEARS so this isn't a sudden shock to my system, but could it still be the reason? This small gain is really diverting my focus, one minute I feel more driven to excel and over come this and the next just wanting to give in and give up.